I have a 99 Chevy Silverado 4wd 5.3 1500. I was driving down the road and bang! The fuel pump went out. Got it done professionally, cost a fortune but it "was done right". They got the truck running and driving but now it is shifting hard between 1st and 2nd gear and between 2nd and 3rd gear. And when you're going about 65 on the highway it stutters like it's in between wanting to down shift and wanting to stay in the current gear. As soon as it down shifts if you hit the gas harder it drives fine again. It's just that in between point that it is really jumps and shakes the car not real bad but noticeable. Im trying to sell it cuz I got a new truck but nobody will pay what I'm asking if they thing the transmission is going out. Hopefully it's not but it had no shifting problems before the fuel pump change. I've heard that you may have to reset the computer because the truck is not used to the higher fuel pressure and the "shift points are screwed up"

Any ideas would help tremendously.
Thanks

 

did you change your gas filter? it cause this because not getting enough gas

 

Yeah they put a new fuel filter in it.