I have a 38 foot Sportscoach MH with ISB 275 HP and 6 speed allison. I was driving in Ohio today (flat land) no wind, and got 11.6 mpg. Discovered that at up to 58mph I was running at 1750 rpm, when I would speed up to 60 mph the transmission would shift and the rpm would drop to 1600 rpm at 60 mph.

Once I had a 40 mph headwind in New Mexico and the fuel milage dropped down to 6 mpg (I could only get a maximum of 55 mph with the tranny in 4th.) Tomorrow, It will be working the mountains of Pennsylvania...I probably will expect about 9.5 mpg.

Sounds about right. What year is your Sportscoach?

Gilbert

A head wind or hills really cuts the miliage on my RV. I have a 58 GMC 38 ft converted coach with a detroit 6. Onthe flat highway towing a car runs about 13 mpg but cuts back considerably on hills. (don't have the gears) it has only a 3 speed alliston with a lock up converter.
When I'm on the flats I'm in the passing lanes. it cruises about 70 mph....
:) Rick