[Jrainman]

I would think you would be getting higher MPGs , I have a 68 c10 daily driver ,when I first bought it it had a 1981 4 bolt 350 .endelbrock carb,373 rear with a TH400 ,I ran it everyday 140 plus miles round trip to work ,with a average of 16 MPGs ,I put about 50,000 on that set up before the head gasket blew, rather then fixing a unknown total milege engine ,I replaced it with a L31 long block crate engine from GM, I also installed a fitech FI system , put a rebuilt TH 200 4R trans in her, and then rebuilt a 71 3.07 rear and stuck that in. my average MPGs are 18 ,but I do drive it at a much higher speed on my 140 plus mile round trip to work and we are talking all highway miles here the truck hardly sees under 50 MPH and 1/2 of that trip im in the 75-80 MPH range . my experience has lead me to think if you are looking for better MPGs when it is time to replace the engine opt to go with a GM LS series engine the LS conversion seem to offer a all around upgrade to these trucks,it does cost more and a little more labor intense but it seems its the way to go these days.