I've had my 32 1/2' Itasca for about 16 months. During that time I've been averaging between 8 - 8.5mpg, not using cruise control, or the dash air, while running the generator on most trips, usually running 60-65MPH. Driving in flat southern/central Florida, where the highest elevation is a highway overpass.
This past weekend I drove down to Key Largo and made a conscious effort to stay below 60mph. I averaged exactly 9 MPG. On the way home, driving the same speed, with the tow/haul mode on (for the first time ever), I averaged 9.7MPG. (it had been 9.8 right before I took the picture).