Chevrolet Repair: GMC 454 vs 350, fuel mileage, gear ratio

Question
I have atruck that is 5 tons, I have a 454 in it now and get 6 MPG.  If I drop a 350 in this same truck, what would my gas millage be?

Answer
Hi David.  mileage would be about the same or less as you are working the smaller engine harder to pull that weight. that of course would also depend on the HP of the 350 you want to install. if you want better fuel mileage say on the highway try changing the rear end gear ratio.