1991 POSSIBLE TIMING ISSUE
 

I have a 1991 Sierra with a 5.7 engine. Just recently had a full tune up put on it with a new distributor. The truck seems to run ok but around 40 miles per hour or so i have a dead pedal and have to push it a long way to speed up and if i let off of it to quick it jumps. The timing was set but does it need to be set at the dealer with the computer to fix this as i have heard or does this sound like another issue all togeather? Any help is greatly appreciated.