Our number of members owning GM diesels are growing everyday. What year and version of GM diesel do you own, what is your average fuel mileage, and what mods have you done to improve it? I have a Duramax LBZ in my 2006 Silverado. My average mileage is 16-17in the city, 19+ on the highway with a 6" lift running 35's and 3.73 gear ratio. I have added 5" Diamond-Eye cat-back exhaust, a modded stock air box (breathes better than stock) and a Godzilla Stealth2 programmer set on 70hp tune (best mileage with this setting).