I have a "engine miss" on my 1995 gmc jimmy. it has a 4.3 vortec engine. I replaced the fuel pump in the gas tank, both oxygen sensors, distributer cap & rotor,spark plugs,ignition wires, e.g.r valve, cpi unit, fuel filter not all at the same time but the "miss" from 1000rpm-1800rpm still there amazingly **SOMETIMES** Ican't figure it out. Gary.

These have problems with injector faults. It will show up as a missfire. Identify which cylinder. One thing I saw that works is to have a true fuel injector cleaning done. This is done by a pressurized cleaner, bypassing the fuel pump and running solely off this cleaner. This used to be the TSB solution at the dealer prior to replacing the injector at fault. Do not let them do the "I.V." set up. All this does is **** cleaner(something similiar to blue water)through the intake. Not always effective. The pressurized system is truely effective. You will notice at least some improvement, if not totally. If it fails to fix the issue, you will be replacing injector/s. The reason this occurs is carbon build up and then the injector drops fluid instead of atomizing. Let me know if you need anything.

Are the fuel injectors firing on all cylinders?
If they are not, it's a computer problem.