I wouldn't get too exited about gas mileage. The factory 454 trucks I had would get a solid 10 mpg, didn't matter if you were going uphill, downhill, loaded, empty. One was throttle body injected with 4.10 rear end no overdrive, another was Q-jet, 3.73, no overdrive. The only other big block gas I had was in a '67 1/2 ton, 396 with a powerglide, in 1971-72 gas mileage was not my main concern, I was just thrilled to have wheels to get to school and work. Now my crew cab dually 4wd 6.5 diesel with 4.10's and overdrive gets 18mpg, 7000lbs empty. I'm happy with that.
