Duramax Lifetime Supporter
Join Date: Apr 2010
Location: Maumelle, AR
18-19 average, 22-24 highway with my 07 Classic LBZ using my custom ~400hp daily tune
Very similar mileage (check sig) on 265 tires. Gotta keep it at or below 2k rpms, though. And yes, that means going around 65mph or less on the freeway. I lose at least 3mpg on the freeway with 60-65 vs 70-75. Heavy truck + drag = exponential force to move it.
2004.5 GMC Sierra SLT EC 2500HD 4x4 LLY w/LBZ MP, PCV reroute, EGR blocked, 4" exhaust, PacBrake TR sleeves, DSP5 & EFI-Live w/Idaho Rob tunes