Drove to work this morning no problems, no dipping RPMs, no rough idling, no CEL so far.
I replaced that IAT plug, and checked all the grounds I could find and cleaned them up with a wire brush. The grounds were not in bad shape, so I am assuming that plug is what was giving me problems. I guess a faulty IAT can cause the PCM to think it is getting too much/too little air. I tested the resistance of that sensor while at 120°F, and the ohms reading was within specification so I left it alone. (3,600+/- ohms)
I did test the fuel pressure while I was in there as well. Key "ON", give me about 43lbs pressure which lowered down to less than 30lbs in about 2 minutes. After running the engine for a few minutes, I got a steady reading of about 40lbs, and it did not lower to 30lbs within 5 minutes, it stopped at about 35/36lbs. So this is a little low spec is 44 to 54lbs, but the leak down was withing spec. I may have a fuel pump assembly replacement coming down the road. For now I think it's fine. It was a rental fuel tester so it could have been off a little too, not 100% sure.
So all in all I was getting false lean condition information which was triggering P0171, supplamented by the computer by dumping extra fuel, which was causing misfires which gave me P0304. Had I seen the plug sooner I could have saved me some time/money/effort. I'm not bummed tho, I traced it down properly in my opinion by IDing a poor condition intake/exhaust gasket, worn plugs/cap/rotor, a shitty connection for the upstream o2 and replacing with the specified o2 (the one i took out was wrong) and replacing an original 20yr old CPS sensor that was caked in road grime. These are all things that needed to be done anyway.
Next time, I will be sure to start with sensor plug conditions, testing them for proper voltage, and checking all grounds. Then go from there.
Thank you Tworley and Jerry B. for the helpful advice, and thank you to everyone else that watched this post and suffered through my long-windedness. Hope yall learned something (or at least learned what not to do
) I'll update this thread after a few days of driving as well, just so yall are up to speed.