WhoCaresAboutMyProblems

I could really use some help with my 04 S10 4.3
I'll try and keep it short as possible. Truck only has 123K miles. I inherited it from a family member with P0170 and 0171 "lean bank" codes. I cleared those codes and the truck ran fine for 6+ months. Suddenly a few weeks ago it began to idle rough and lack power (it already lacked power and had fairly bad MPG IMO) and so I began detective work on the internet. Commonly mentioned was the intake gaskets, so I did that job. The truck didn't get better, in fact then it began throwing a "rich bank 1" code instead of lean bank and so I moved into a few other things and those have still not helped. I will use list form for the things I've tried.

0. When i first got the truck I noticed one vacuum line was really bad and so I replaced all of them except 1 that I couldn't reach. (attaches to top of transmission area and I can't get my hand in there, it goes up into engine bay and attaches to a Tee junction IIRC)
1. Intake gaskets upper and lower (properly done IMO after watching at least 5-6 quality YT video walkthroughs) Used a high quality Fel-Pro gasket kit.
2. That included new gasket around the fuel injector spider as well. These gasket jobs didn't seem to change anything on the truck
3. New O2 sensor on the bank 1 side where I was getting the error. No help.
4. New MAF sensor. No change.
5. New fuel pressure regulator (basically re-doing the spider gasket again as part of that process since all that has to come apart). No change, or the truck seemingly got even worse.
6. I have used carb cleaner and sprayed around the top of the engine and vacuum lines to check for air leaks but didnt really notice anything changing the engine behavior while spraying.


Idle is REALLY rough now, moreso than when the problem first appeared I'd say. Rich bank 1 code persists, and then got a cylinder 1 misfire code too, which had never been there before.

Things I haven't tried but have no idea if i should waste the money on.

1. Another O2 sensor on the non rich bank side.
2. PCV valve (this one rattles just fine like many videos say it should)
3. Spark plugs and wires and/or distributor stuff.
4. Smoke test
5. Fuel filter or fuel pump stuff.
6. Spider injector (I was tempted to make this my next step TBH but I didn't want to waste $200+ on it yet)

My knowledge of this system is just basic and I'm a "learn as I go" type of guy. This is my first Chevy product. I'd love to avoid taking this to a shady mechanic whos going to tell me its some crazy BS when really its just a vacuum line or something. I just dont know what else to do next.