Since I have to commute 112 miles per day for a while in my 2001 F350 (picture below, for stance, and tire size) I filled up completely (topped off, full full), drove about 40 miles straight shot on the freeway. I kept the cruise control at only 60MPH, with a few variances due to traffic. Jumped off the freeway, filled up again, she got 15.3 MPG.
The truck has 103K miles, banks chip, banks cat back exhaust, banks trans command module, is in pristine condition and is impeccably maintained.
The truck has 3.73 gears, and was turning about 1600-1700 RPM almost the whole time.
The truck was barely working. The EGT was 400-450, turbo boosting hardly at all. (except up a mild hill or two, 5-10 PSI for a minute or two)
With a straight shot, low RPM and very low EGT's, I would have expected 17-19 MPG. Any comments?