I think alot has to do with two factors:



1. Front air dam in good shape. Wind underneath a truck acts like an air brake.

2. E load range tires with 50psi in front and 60psi in rear.[recommended pressure is 45psi in front and up to 80psi in rear depending if towing or not] These tires make a tremendous difference over lesser tires in handling the 5700lb Sub.



Also I have a two wheel drive with 3.73 gears [stock] If they go to larger tires fuel consumption will go up dramatically.



When I drove to Denver in February and then again on the way up last week [not pulling anything] I got 17-18.5 @ 75mph with the AC on. When I went ot FWB last April I got the same with the AC on. I have asked three other C2500 owners I know personally and they get the same mileage. All are 1999 models with the same motor. Another key is to keep your foot off the gas...no sudden acceration!h



good luck,



thom