How do I tell if my plugs were replaced?

Well, if you still have the original plugs, it would stand to reason you got screwed. Get something in writing from the second mechanic or a dealership these are original plugs and not new iridium plugs, then take the first guy to small claims court (be sure to have your invoice for the work done). File a BBB complaint as well, and take it to social media like Google reviews. Your first mechanic sounds like a cheat.

Thanks Ken. I haven't been able to confirm that the 3 white dots on top actually signify factory plugs from GM. I'll check with a GM dealer.

What plugs are in there now? Originals are AC Delco, BUT the original part # that IS stamped on each plug are no longer available. If it's AC Delco brand plug that's in there and it's not # 41-103, then it's the original plugs. 41-103 replaces the original and should be the only plug put in our I6 engine.

Did the second mechanic find what was causing the rough idle or misfiring? It could also be plug wires, coils, cap or rotor, etc. If he swapped out plugs and that fixed the problem it would lend credence the first guy cheated you.

Yeah, he changed all the plugs and he did 3 of the coils and cleaned the throttle-body. Gonna do the other 3 coils as soon as I get the $ together. The weird thing is, it just had a small miss at idle when I took it in to have him replace the thermostat. He had to disconnect the battery because he had to take the alternator off. When he was done, it was running rough as hell. That's when we replaced the plugs, and it was still running rough. Then the engine was throwing a code for cylinders 2 and 5, so we replace those coils, and it was better but still rough and throwing a code for misfire in cylinder 1. So we replaced that coil, and it's back to the way it was with just the small misfire at idle. Get's more pronounced with the A/C on. It's strange. When it gets hot, sometimes it will start to shift hard into second gear. But, if I turn it off and restart it, it shifts fine. The speakers only work on one side of the car, but will occasionally kick in on the other side...Just randomly. My cruise control only worked occasionally until after he did the thermostat, and now it works every time. I really think it's something electrical, but gonna worry about that later after I get the other 3 ignition coils replaced.

The plugs are marked 41-103, but they have the 3 white dots on top. Does being marked 41- 103 mean they are NOT factory plugs??

My 2004 is doing the same thing but after I replaced thermostat it got worse and I only replaced the plugs and coil 1. Now it’s showing the code for random misfire. Anymore luck with urs. When I run my ac it will die when I stop after running rough for a few.

I have done research and found that when you do the throttle body, plugs, coils, injectors ,thermostats, sensors,,one thing in common ,,if you disconnect the battery and it clears or wipes the computer too,,it will run ruff for a week or more until the computer learns the idle speeds,,,and eng driving habits etc,,,so if I was you try that if it wont harm the eng or find a good mech who can help you with this problem