I think my 7.8 mpg is as good as it gets for my truck. I just had the heads rebuilt and replaced the rings. I've driven my truck from Maryland (near Washington DC) to the middle of Kansas and I believe the gears are as tall as possible based on the available power. If you had a larger HP V8 you would have to calculate the gas consumption based on the same rpm I'm turning now. So the question is, what kind of milage would a BBC get turning 3500 rpm all day long?
I remember hearing a BBC in a Suburban only got 10-12 mpg whether they were pulling or running empty, so I don't think a big truck would do better then that.
Your mileage may vary...
Mike B
