Join Date: Nov 2000
Location: Madison, Wisconsin
Feedback Score: 0 reviews
Back when my PSD was my daly driver, from 120 to 150 miles per day I got around the same MPG's as you, 18-1/2 to 19+ MPG, even got 20 to 20-1/2 MPG average one summer over 10,000 miles of driving. In winter with 10W-30 oil, a winter-front, and using the block heater every morning I'd still get 17-18 MPG, so blended fuel costs you 5-10% on your MPG.
Like others have said, make sure you dont have a brake dragging, feel your drums & rotors after 30-40 miles of highway non-stop driving. You probably won't like it but I bet your chip has a lot to do with the drop in MPG's. It takes more fuel to make more HP no matter how you do it.
'96 F-250 Reg. Cab 4X4 5-sp POWERSTROKE
298,500 mi & NO Problems, LUK Clutch