I just got back from a 4700 mile trip from Portland, Or down throughout the SW , 4 courners, New Mexico and Colorado back through Montana Idaho, BC and home. I'll tell you I honestly think the type of fuel has a lot to do with the mileage - see the article on the main BB. But I just can't seem to figure out which type gives me the best. I didn't tow anything on that trip, have an above cab Shell - not a camper, have 3. 54, auto, VA plug and power and I averaged 20. 37 MPG. I actually hit 23. 8 going 266 miles from Cortex, Colo to Santa Fe! However when I get back home, I always seem to get between 18-19 - which is mostly in town. When I take long trips, say to Spokane and back, about 700 miles roundtrip, all freeway and driving like I did on the big trip - I never break 20! The only thing I can think is ONE - Higher Elevation, I was running a lot at over 3000', or different fuel! What does anybody think - and by the way I don't baby the thing - I run it usually about 75. However when I got the 23+, I couldn't go that fast because of construction and traffic.