^^^ This guy is spot on! My old girl on the way home got 14.3 MPG... I know I know, you would not believe me. Here is the trip. London, KY to Fairhope, AL. Through Knoxville, Birmingham and Montgomery. Very light and towing
nothing. 62MPH max and if you look, it is mostly downhill.
Have not had a big trip yet as I got very ill and have not as yet loaded her up for a trip.
'92 Gulf Stream Sun Voyager. Tweaked 5.9 Cummins, complete interior makeover (previous owner).