I have a F350 C/C, long bed, 3.73's, SRW 6.0 PSD with 11,000 and auto tranny. At 70 on the highway I get 16-18 with #2 and 13-16 with #1. I would probley get better milage if I could keep my right foot from having those darn downward impulses. Almost half of the highway driving is up/down and around the mountains. Best milage ever was driving conservative at 60-65 and easy on the pedal (20 mpg).