00 Jimmy Misfire after warmup

2000 Jimmy V6 4.3L 4wd 130,000 miles

Second occurrence of this problem. First time, driving for 8 hour trip made it only 2 hours before loss of power and SES light flashing. Sounded and felt like it was misfiring. Stalled after 3 miles wouldn't restart. Towed to dealership, told me to do full tune-up (but didnt do it per my request). They cleaned fuel injectors by running a chemical thru it which in turned clogged my CAT, had that removed and ran a straight pipe. It would run but very rough (misfiring) so I tried driving to my destination but only made it another hour before it died again. It would run at idle (misfiring) but not enough power to drive. Had it towed to destination where we did full tune-up. Plugs, wires, cap, rotor, coil, and air filter. Started right up and ran GREAT. Drove it around that area for about an hour, no problems. Drove another 8 hours back home with no problems. After another week of minimal driving...no problems. Now if i drive it more than 20 minutes and shut it off then restart it begins misfiring again. Took it to auto parts store and ran codes. Misfire on cylinder #6 and MAF sensor. It runs completely fine for the first 20-30 mins (after sitting for about 24 hours) and has yet to act up without shutting it off. I don't want to drive to far so I'm not sure if problem will occur if i leave it running. I have checked the wires, disconnected battery, and tried leaving the MAF sensor unplugged and nothing has made a difference. Thanks for your time.

If you drive the truck with a misfire, that unburnt gas gets into your convertor, overheats it and ruins it. Driving even for just a few minutes could damage your convertor. Secondly if you have no convertor on it now, you will get a SES light on as a result of not having a operational convertor on there, just so you know. Also, if your having a MAF sensor code popping up, try cleaning it with some brake cleaner and re-installing. Either way if you have a MAF problem you need to get that corrected before you can chase that misfire. Also did you use an AC Delco cap/rotor? The reason I ask is becasue aftermarket cap/rotors have seemed to have caused problems for many people on here.

Yes, the CAT became clogged and I had it removed and ran a straight pipe as opposed to $800. SES light did not come on after over 500 miles of driving without converter. I replaced the MAF sensor a couple days ago and it is still doing the same thing (minus the SES light). Today I removed spark plug 6 and 4 to compare and 6 was SLIGHTLY more "burnt" than 4 but neither looked worn nor damaged. Regardless I replaced spark plug 6 with brand new. Quadruple checked the wires and pulled them further away from block as recommended to avoid the possibility of heat damage. Let it run idle for 5 minutes, drove it for 5 miles, parked it (was running a total of 23 minutes), shut it off, started it back up and let run for another 2-4 minutes and the truck started to misfire again. No SES light. Against my own personal belief I am going to replace the cap and rotor with Delco parts (Duralast on it now) since my patience has worn thin and I seem to have run out of options and advice. If (most likely when) my truck decides to act up again is there any other suggestions? Thank you again.

Ignition Control Module?

Also, if your having a MAF sensor code popping up, try cleaning it with some brake cleaner and re-installing.

Won't brake cleaner destroy a MAF? I know carb cleaner will, but won't brake cleaner basically do the same thing to it?

Got my money on the "Doesn't last" distributor cap. If you have AZ wires, lose them too. AC Delco or Autolite Professional series wires only. Make sure you use AC Delco platinum plugs only. Cheap parts are not good, good parts are not cheap. With all that snow and rain you've been getting in Macomb county lately, secondary ignition problems show up real quick.