Mine gets 10 mpg. It is paid for and has a big block 454.
Guardrail
I have an antique, (mid seventies) 3/4 ton wood hauler with a 454. It also gets about 10MPG but I drive it less than a thousand miles a year. I can stack wood to the top of the cab & it doesn't even grunt. I can haul in one load what many others haul in two loads. "Ole Blue" has been here so long he is one of the family.