I had a 2005 2500 with the 6.0. It did pretty well towing our 7500# boat/trailer. We got 8.1mpg going from Phoenix to Lake Powell and 9.4mpg coming home (mostly downhill coming home). Not towing, we would get about 13-14mpg average per tank. We went to a duramax crew cab and I would have trouble going back to a gasser.