A lot of erroneous assumptions by the OP. It takes work to move 8,000 lbs. or any amount of weight at 65 MPH and even more to pull it up a hill. Work equals fuel burned.
Automatic transmissions provide better fuel economy without exception. With 6 and even 8 speed automatic transmissions the engine is running more of the time with the power band where it is most efficient. This applies equally to the tractor rigs that are moving to automatic transmissions to maximize fuel economy.
Want fuel economy get a Casita or similar trailer and tow it with a 30 MPG Subaru Forester or similar small SUV.
I refuse to believe that fuel is "expensive" when less than 1% of the drivers I see on the highway are doing anything to improve their fuel economy. How many people, even those towing, do you see at 65 MPH? How many people are towing huge 13,000 lb. 5th wheel trailers or driving Class A motorhomes towing a car?
The higher fuel prices go the better as hopefully at some point less will be needlessly wasted by people and we will not need 250,000 troops stationed overseas to keep the oil coming.
