Our friends at HitchAnything.com sent us some information they collected from their patrons. In December HitchAnything conducted a survey open to its regular customers who tow; we thought you might want to see the results.
While it's not the most scientific survey, it offers some pretty good information about Cummins, Power Stroke and Duramax fuel economy and fuel costs when those engines are used to tow. The survey even asked regular half-ton and midsize pickup truck owners a few questions as well. See the info graphic below.