[Eddie H.]

With a stock 350 and automatic trans, these trucks were good for 10-12 MPG when they were new. You could add fuel injection and an overdrive , and might be able to bump it up to 14-16. Remember that you're dealing with 50 year old technology and the aerodynamics of a storage container. You can make a lot of horsepower with a 350, but I wouldn't expect much in the way of fuel economy.