Sputtering after car warms up ,seems like a misfire every so ofte

Need a fresh start at a repairs shop
Was no need to install any of those parts
You needed to diagnose any and all issues
first,then come up with a solution to repair

Do you have a check engine light on?

- Check engine compression.
- Check valve clearance.
- Check spark plug gaps. (0.8-0.9 mm).
- Check vacuum leak at intake manifold.
- Fuel pump pressure too high.

Sound like you may have a catalytic converter plugging up. Take it to a muffler shop and have them check it for you.

CLOGGED FUEL FILTER OR CLOGGED FUEL INJECTORS.WILL CAUSE SPUTTERING AND MISFIRE.LEAKING EGR VALVE WILL CAUSE ROUGH IDLING SPUTTERING.

1 Inspect Distributor Cap and Rotor Kit Loose, Cracked or Worn Distributor Cap. 1 Inspect Wireset Worn or Damaged Spark Plug Wires. 2 Inspect Distributor Cap Loose, Cracked or Worn Distributor Cap 1 Inspect Condensor-Ignition Faulty Condensor-Ignition. 1 Inspect Timing Specification Incorrect Ignition Timing. 1 Inspect Timing Specification Incorrect Ignition Timing. 2 Inspect Spark Plug Fouled, Damaged, or Broken Spark Plug(s). 3 Inspect Distributor Worn, Damaged or Faulty Distributor.

Replace the fuel filter.

Maybe bad plug wires or cap and rotor. I'd replace.

Check the injectors. They are really bad about leaking on the 4.3's.

next time it does this, try spraying wD40 on the distributor, all around it. if this fixes it, you have a crack in the distributor cover. just replace it. good luck