wow a 454 in a 1 ton.I have a put together 1 ton Suburban,,(no GM never made one in 91') as the previous poster had said is everything has to be right to get the best mileage and even with you getting the ''best' mileage that truck can get its not going to be great,maybe not even good.
mine,(well i have not even tried to ck mine..lol)..is as right as it can get and i have become very good friends with the Shel station just around the corner from my house.