I have a 2001 24' Winnebago with the 8.1 liter engine. The motorhome weighs 11,500 and I tow a 3,000 lb. mini pickup truck. I have kept track of all of the gas that I have put in it for almost 8 years now, and my long term mileage over all kinds of terrain is 8.9 mpg. I drive it pretty carefully, and rarely exceed 65 mph.
I have the same unit as Alan but I don't tow. Down hill with a tail wind I can get 10. Usually 9 to 9.5 as long as I remember to change or clean the air filter.
As I thought. The lower the weight, the higher the MPG, especially wit hthe torque the 8.1 generates. I should (fingers crossed) get around 8 mpg.
I am still negotiating for the unit, so I hope to see every one on the road, especially at Gillette.