Did you ever figure out the oil pressure issue? I am experiencing exactly every symptom as you, cold it runs at 35 to 45 psi depending on acceleration, once warm it doesn't go up past 30 even at full throttle and at idle when warm it goes as low as 10 to 15 psi and the engine is thumping. I've changed oil pressure switch, the screen under it, the oil pump, and the oil pickup tube o ring. None of these things changed any of the symptoms.

 

Hi! I think it’s been about a year since this started happening, and it still is happening. I eventually installed a performance oil pump, and although that keeps the oil pressure high, it didn’t solve the problem. The car still misfires at idle. I suspect at this point after replacing everything I could think of that maybe a lifter is going bad and maybe even the cam will need a replacement/upgrade. However, although this issue is annoying with the engine thumping and all, I’ve managed to put about 8,000 miles onto the car with the issue present. I’ve driven it from Phoenix to Las Vegas and even to Rocky Point, Mexico and back without any issues. At 185,000 miles now, it still does good for roadtrips and highway drives, it’s just uncomfortable in the city since it misfires at every red light (also I still don’t have a lifter tick!!). The transmission is going to need replacing sometime this year, and once that goes, I’m probably going to work on the engine too. It’s sad to see such good engines become garbage because of GM’s stupid AFM feature, which seems like the source. New lifters/cam might be the way to go, but I can’t confirm that until I try it myself

 

If you're in Phoenix, I might recommend taking it to Blackwell Automotive at 40th Street and Greenway.

 

I replaced the screen. Same issue. Not sure what to do next.