Just returned Round trip from Bakersfield to Sacramento and San Jose last weekend. For the 750 miles total, I hand Calc. 19.1 MPG. running about 75 average, turning 1,600 RPM in Overdrive + the Gear Vendor Overdrive.

If I start crusing @ 80 or 85 the milage really takes a dump.

 

I also noted that @ 75 MPH, 1,600 RPM on flat ground(I-5), empty truck (except for 100 gallons of diesel at the start and about 300 lbs. of tools, I was running 5 PSI of boost and 650F on the TITemp., and 140 on the transmission temp..