Words by Mark Williams, Photos by Mark Williams, Mike Levine, Ian Merritt
It's not that we don’t trust the big-truck manufacturers when they set up towing exercises during their new-vehicle introductions — we just know we’re likely to learn a bit more about a given hauler when we take it on the road. That’s just what we did when GM tossed us the keys to its newest top-level one-ton hauler, the 2011 GMC Sierra Denali 3500 HD dually.
Naturally, we wanted to give the revitalized Duramax — which makes 397 horsepower and 765 pounds-feet of torque — a decent challenge for this exercise, so we searched for the right environment with plenty of tough hill climbs. The more we thought about it, the more obvious the answer became.
Of course, that meant a nice, long road trip through Colorado, weaving up and over the Rocky Mountains as many times as possible. In no time at all, our route would hit six different mountain passes getting close to or climbing above 11,000 feet in elevation, including the highest paved road in the U.S.
To make the trip interesting and to isolate the Duramax’s strengths and weaknesses, we needed a fair amount of weight behind us. We found that in a Colorado travel trailer loaned to us from K&C RV in Longmont, Colo.
For those astute PickupTrucks.com readers who may recognize this GMC Denali HD from our 2010 HD Pickup Truck Shootout, you’ll notice our trailer is somewhat different from the engineering trailers we used for that Shootout.
Our Dutchmen Colorado 32RL fifth-wheel trailer was close in weight to the trailers our one-ton diesels pulled up the 7 percent and 16 percent grades during the Shootout, but our fifth-wheel trailer gave us a more real-world feel with its 12-foot-tall profile standing high in the wind and a realistic center of gravity.
With the tanks filled and our gear stowed, our trailer tipped the scales just over 11,500 pounds with a price just over $45,000, bringing the total of truck and trailer just a tick under $110,000. We knew the total weight of our Colorado was far below the 3500 Denali’s maximum rating of 21,000 pounds, but it would still allow us to get some good feedback.
Our plan was simple: take five or six days to circle some of the most interesting terrain the state of Colorado has to offer while hitting as many high-altitude mountain passes as possible (without sliding off a cliff) to see how confident and/or comfortable the new powertrain is while pulling a hefty load in thin air and steep inclines.
Pulling the Eisenhower Tunnel
After picking up the Denali and trailer in Denver and visiting our friends at ATS for some quick dyno runs, we started our towing test by taking our 19,000-pound, 55-foot pickup and travel trailer to the Eisenhower-Johnson Memorial Tunnel, about 60 miles from Denver.
We ran the truck and trailer up and down the grade between Georgetown and Dillon, the two towns on either side of the tunnel, whose highest elevation is 11,158 feet. Of course, to get the number of unencumbered runs we wanted, we did this late at night, but it gave us some valuable information. For example, the Duramax doesn’t really care at what altitude you’re pulling a load -- it likes to run.
On several of our 7-percent-grade runs from Dillon to the mountain top, we topped out at 66 mph over the seven-mile trip. The Duramax and Allison transmission, especially when in tow-haul mode, does an excellent job of holding the climbing gears up to and over 2,700 rpm before shifting to a lower gear. The result is more climbing power and speed during stretches when we could go wide open throttle.
Likewise, on the downhill grades we appreciated the same amount of intelligence from the Allison six-speed transmission’s control module, as it allowed the grade braking software to downshift into another gear every time we touched the brakes, revving the engine up to a lofty 3,700 rpm when necessary.
The Sierra’s new exhaust brake, when engaged, helped slow down the hauler a touch quicker than without it. Although the exhaust brake is not for everyone, we’d like to hear it make a more noticeable tonal change. Our other complaint is that there is no way to see exactly which gear you are in at any given time unless you have the Allison in Manual mode. It would be nice, no matter what your preference, to see how the gears are working like in the new Ford Super Duty.
We also tried a few runs with a giant 16,000-pound, 39-foot Cimarron Horse Trailer loaned to us by Transwest Truck Trailer RV in Frederick, Colo.
By the time we finished our hill-climb runs (at 3:30 a.m., ugh), we were ready for bed.
Rocky Mountain National Park
From the Eisenhower tunnel, we headed north on U.S. Highway 40 over the Berthoud Pass — which is a few hundred feet higher than the Eisenhower — to Fraser, typically one of the coldest places in the Lower 48. The Denali pulled like a champ up the two-lane climb to the pass, and then it allowed us to control downhill speed easily with a few quick touches of the brake. We ran in tow-haul mode every moment the trailer was hooked up and found ourselves manually activating the exhaust brake when necessary.
It’s worth noting that our towing mirrors could manually extend about four inches to give us just enough visibility to see past the width of the trailer, but we would have liked a little more. Also, the lower wide-angle mirror gave us plenty of width to check our trailer wheels as we swung both wide and tight corners. We liked that the upper mirrors can be electronically controlled from inside, but we became frustrated whenever we needed to manually reset the lower convex mirrors.
Heading into Rocky Mountain National Park was exhilarating, especially after we got through all the construction stops and single-lane escorts leading to the top of Iceberg Pass at 12,183 feet. At more than 1,000 feet above the tree line, the terrain looks more like Alaskan tundra than the highest paved road in the Rockies. The views are spectacular and road is narrow, and we spotted quite a few very, very cautious drivers (which, we suppose, is better than the alternative).
Quick piece of advice: Between the summertime construction and driving habits of most elderly tourists, give yourself plenty of time to see this park, whether you’re pulling a trailer or not. Likewise, at that altitude, expect all the non-turbo gas engines to run out of power pretty quickly on the way up and down the mountain.
Once through the national park, we headed to lower elevations through Estes Park and into Fort Collins. We noticed a few gear shudders between 2nd and 3rd, and between 3rd and 4th when our speeds sat right in between the gears — almost like the transmission wasn’t sure whether we’d pick up speed soon or slow down. We assumed the vehicle hadn’t quite learned the subtleties of the trailer weight quite yet, but the shifts and transmission line pressure were a little harder than we would have liked.
Onto Steamboat Springs
After a quick dinner with family and an overnight at a local RV park, we headed up the Poudre Canyon Highway (Colorado State Highway 14). This road winds along the Poudre River, following the steep, walled canyon with large rock overhangs that big-rigs with tall trailers and motor homes need to watch out for. Without much traffic behind us, the Denali lumbered along in 6th gear at 1,400 rpm as we gently climbed upriver.
Our vehicle came equipped with a navigation system and encountered only a few hiccups, as some new roads didn’t show up on the mapping program. Also, it would have been nice, especially for this trip, if there was a way to keep track of our altitude climb or exact elevation. We also couldn’t figure out how to get our GPS coordinates from the navigation system.
Once we made it to the rural town of Walden, we continued on Highway 14 until we met up with Route 40, crossing the Continental Divide of the Americas as we made it over Rabbit Ears Pass (at 9,500 feet) and into the Park Mountain Range. Although not steep, we did climb from the 7,500-foot North Park Plateau out of Walden. According the GMC’s on-board computer, we were averaging 11.5 mpg. Not bad with the high-profile trailer, but it’s worth noting we weren’t breaking any speed records, either. Our average speed on most of the straight highways was right around 60 mph.
We found the Denali’s “miles to empty” readout especially useful as we ran our truck on diesel fumes, thinking we could make our first fill-up of the trip in Steamboat Springs. With about 30 miles to empty, the system goes into a “low fuel” mode and automatically shows all the fuel stations on the nav system. We made it to Steamboat Springs with a few miles to spare, yet still had more than a gallon of fuel left in the tank (34.6 gallons at $3.03 per gallon for $105 for the fill-up). Our odometer reading was a tick over 400 miles.
The run out of Steamboat Springs — a very active mountain town with incredibly narrow downtown streets because of construction — was also relatively flat, so our run to Craig and then south to Meeker along the White River also got us good fuel economy. By the time we pulled into Meeker — famous for its big-game deer and elk hunting — we were beat and still registering a full tank of fuel.
We found an RV park just outside of Meeker, disconnected our rig and headed into town. If you’ve never handled a fifth-wheel trailer, it’s easy to see why people like it. If you have the right truck, it’ll tow your house behind you, yet still allow you to drive your own pickup truck into town. Just set up the trailer, level it a bit, disconnect a few links and a hitch lever, and you can pull out and leave your kitchen, bath and bedroom at your campsite. Our first disconnect took us about 15 minutes (most of which was spent talking as neighbors came up to lend a hand), but as the trip went on, we cut that time in half.
The Grand Junction Gateway
The next day had us continuing south to Rifle, then to Grand Junction (off Interstate 70), then down U.S. Highway 50 toward Montrose. Grand Junction has long been a jumping-off point for 4x4 and ATV enthusiasts, with many off-road and biking trails. You also can’t drive a highway to Delta, Montrose or Ridgway without seeing (what seems like) dozens of RV parks. This is a popular stretch of road for RVers, and our rig looked right at home.
The drive from Grand Junction south to Ouray (pronounced “YOUR-ray”) is one of the most spectacular drives in the world, giving you a taste of just about every type of scenery Colorado has to offer in just 80 short miles. You’ll see vast prairies, shrub-covered rolling hills, river-cut canyons, forested mountainsides and steep mountaintops that wall in around you.
Most of the drive to Ridgway was on relatively straight highways and good pavement; however, it took us a few days to realize that we weren’t experiencing the fatigue we typically feel on long trips, even though we were pulling a big trailer.
Eventually we realized that whether the truck was loaded or empty, the new, heavier-duty steering box that GM fits into the new front end on all models makes directing the big truck — and the heavy load behind it — a stress-free affair. The truck tracks well; it stays on center, does not overboost small adjustments and offers little wander. It may seem like a minor detail, but we can’t emphasize enough how important a good steering box can be for long-haul driving, especially when you’re towing another 35 feet behind the bumper. No doubt the dual rear wheels help stabilize the load, but the 1,500 or so extra pounds over the rear axle didn’t affect front-end comfort or feel in the slightest.
We also want to make note of the Denali’s interior comfort. Clearly, this premium package is meant to compete with Ford King Ranch and Dodge’s new Laramie Longhorn edition. The truth is the Denali package probably doesn’t go quite far enough in the name of a separate and unique look and quality level. Still, there are chrome accents, decent wood trim pieces and subtle stitching and material upgrades. Is that enough to be GM’s top-of-the-line? Probably not, but we’re not complaining at this point. We happen to love heated and cooled seats but would have liked a more commodious or compartmentalized center console with different cubbies and hidden storage, and maybe even a bigger glove box. When trying to live out of the cab of the truck, we kept piling things — tools, toilet paper, Gorilla tape, zip ties, maps, baggies and more — into the single-holed center console, which made finding them later a challenge.
The San Juan Skyway
Probably the most exciting stretch of our trip came on U.S. Highway 550, called the San Juan Skyway, just after leaving the quaint mining town of Ouray, heading to Durango.
The climb to Red Mountain Pass (at 11,018 feet) is on a narrow, two-lane road with no guardrails to protect you from the steep, 1,800-foot cliffs just over the white line. The U.S. Department of Transportation won’t put rails up because it would prevent snowplows from being able to push snow over the ledge and could catch snow and debris during an avalanche. The result is a high-anxiety ride out of Ouray that requires all vehicles on the road to pay close attention to all their tires. We should also note there are oncoming semis that love to ride on top of the yellow line.
As you might imagine, we couldn’t take any pictures during this stretch. The width of the dually and fifth-wheel trailer had us constantly checking our side mirrors and the precision of our steering wheel. We’d be lying if we said we didn’t think about what it might look like to drop a trailer wheel over the edge, and then slowly get dragged over the mountainside.
The backside of the mountain puts you on the opposite side of the valley, so our vehicle was against the hillside — clearly a much more relaxing place to be. At the bottom of the hill, we found another old mining town called Silverton and explored some of the old dirt roads behind the town.
This time of year the hillsides explode in the bright yellows of the quaking Aspens and other fall colors. And during our dirt-road climbs, temperatures in our crankcase and transmission were all within spec, as the Denali’s digital gauge readouts allowed us to keep a close eye on the internals. The only gauge we felt was missing on the trip was the turbo pressure gauge, to let us know when we were on and off boost.
Outside of Silverton and back on the San Juan Skyway, our last hill climbs before Durango were Molas Pass (at 10,910 feet) and Coal Bank Pass (at 10,640 feet), where we found several other older heavy-duty pickups dealing with some puking radiators. We offered some help, antifreeze and water and got back on the downhill road to Durango, watching our fuel economy climb to 13 mpg.
Into New Mexico, then Denver
From Durango we headed east, taking a short detour to Chama, N.M., after hearing from a few locals about the climb up Highway 17. Chama allowed us to cross the continental divide once again and head from the 7,000-foot plateau between the two states and climb up to another 10,000-plus-foot outer edge of the San Juan Mountain range.
Chama is an old train stop on the famous Cumbres & Toltec Scenic Railroad, America’s longest and highest narrow-gauge line and a very cool place to explore. In the short time we were there visiting an old friend, we saw dozens and dozens of good-condition old trucks in several scrap yards. We hear there are some amazing mechanics in town as well.
The run up Highway 17 follows the train line, climbing almost 3,000 feet in just a few miles. The highest point, at 10,230 feet, is La Manga Pass, which, sadly, became our last high-altitude pass on our trip. After the pass, we knew it would be all about grade braking and low-rpm, high-mileage flat-country cruising.
We pulled into Colorado towns called Alamosa, Salida and Canon City, all while loping between 1,400 and 1,600 rpm for almost 200 miles. (Thank goodness for XM radio.) With the terrain so flat and no one in our way, we found the 3.73:1 gearing and 6th-gear overdrive (at 0.61:1) to do a good job of keeping fuel economy around 12 mpg when moving at 65 mph. Not great, but not so bad for such a huge truck and trailer combo, either.
As near as we could tell, the engine and transmission got smarter about holding gears on the downshifts and when to make the upshift early enough when ramping up speed. And we hadn’t noticed the rough shifting from 2nd to 3rd we noticed earlier in the week. Likewise, it seemed as if when we were on extended flat sections, the transmission was getting quicker about getting into top gear.
Our final fill-up (before heading into Denver to drop off the fifth-wheel and the Denali 3500) came in Colorado Springs, where we discovered that we averaged over 12 mpg in the last of our three tank fill-ups, with the trip odometer reading 421 miles.
All wrapped up, we filled the tank three times, logged more than 1,200 miles, paid over $322 for fuel and averaged 11.8 mpg on the entire trip, the most of which was done with our fifth-wheel trailer in tow. Admittedly, we were a little sad handing over the keys but had to smile a little bit, knowing we pushed the new Denali HD over some nasty passes and rough stretches of road and nothing surprising happened. By our accounts, it’s not a perfect truck, but for hauling up and over the Rockies, it gets pretty close.
Special Thanks to:
K&C RV Center
14504 I-25 Frontage Road
Longmont, CO 80504
Re: Dutchmen Colorado 32RL
Transwest Truck Trailer RV
7550 E. I-25 Frontage Rd.
Frederick, CO 80516
Re: Cimarron horse & bunk trailer