I have a GMC Sierra 1500 3.0 Duramax, 18000 miles so far and i love it. Had a PW that was averaging 12 mpg around town and 7 towing, I really didn't need a 2500.My GMC id averaging 23 mpg and 15 towing the same enclosed trailer. Both trucks are running about a 35 in tire. My best milage was...