10MPG out of a 400, 66chevy thats real real bad, maybe you need to do something to try to double that number, put in a standard overdrive tranny and change your axal to a 350 gear ratio, or try a 4 barrel carb instead of a two barrel or go get a tuneup.

One time a guy who was a plumber told me a story about his work truck he had a 2003 chevy full size van that he used and was getting 12MPG out of the modern fuel injected V-8 engine in it.
So does it pay to buy a newer truck when you hear crazy stuff like that.?
Thats why I like stovebolts smile