Mine is an 01, dually, 4x4, crew cab, long bed, 4:10 gears, AFE Intake, superchips tuner in tow safe mode, 4" turbo back exhaust, WW, alcohol/water injection and the sonax shift kit.
I get 11mpg around town empty, 12mpg highway empty, 9-10 towing my 13,500lb 5th wheel. always in OD at 70-75mph.
It's always been this way since new, so I can't compare to stock.
I am wondering if the TW chip will make it any better?