2003 2500HD 8.1/Allison/4.10/4x4 since new 11.0 overall with about 8000 miles (about 2500 miles towing an 8500 pound fifth wheel); freeway without air on is about 17 at 65mph, with air about 15-16. Mixed around town/freeway 13-14. All numbers are from the computer.

 

'02 SCSB Z71 w/ 5.3, bone stock- 15.5-16.5 in mixed city/highway driving. I never have really kept track of the milage on the highway, but I tend to drive moderately fast (80 or so mph), so it's probably not much better.

 

My 6.0 2500HD ECSB was consistant avg 11.0 ish, my 04 GTO gets 29mpg highway cruising 70mph. AVG fuel economy for my GTO is 14.5-17mpg.

 

Mine sucks, 14.8 according to drivers info centre, mostly city driving. Truck in signature.