In like vehicles this is true. My might even get 2mpg better if you have 97 1/2 ton Xcab with a Vortec 350. But your TBI 350 in a 2500 is NOT going to get better mpg than your 97 Z71 truck. Manual trans or not. I'd say at best, it might work out to an even wash. Gas keeps going up again, I am likley to end up with another Yota Rolla 5 speed. That car got 33 in town up to 42 hwy, and consistanly got 39-40 hwy. It even got 37 at 90-100mph on m trips from OKC to Laughlin. Running AC hurt it a bit though. I only 30-31 in town using AC. I need that kind of mpg when gas is this high, and sadly, the money I'd save in fuel makes the car payment, so its like driving a free car. I'd rather find me a 3cyl Geo Metro and get 40mpg in town and better on the hwy. I don't get out to my dads much to work on the 2 brown trucks cuz of high gas prices. It sucks.