| Winter blend fuel will net lower mpg, but shouldent be as low as you are saying! but usually winter fuel starts showing up around oct. Dose you truck have a cat on it ( some 03's did)? it could be sooted up pluging it! It seems like you had all the most common problems checked out! Also if you are running the ultra low sulfer diesel fuel (ulsd), it will lower mpg a bit also from the old fuel.
Good luck,
Caleb
__________________ Caleb 05 D/ZF Reg. Cab
PPE GT 4094r, ATS CP3X2, Best ET-12.53@ 109MPH 5/08
Stock Turbo, ATS CP3X2, Best ET -12.91@ 106MPH 10/08
Under the knife to attach a second turbo
04.5 D/A CC/SB- SCIV w ATS 5star converter,Mike L cooler
Stock Turbo Best ET 13.53 @ 103Mph @ 7300lbs
Waiting install of GT4094R |