5.3 oil pressure issues (HELP)

[93 Krawler]

Earlier this year I pulled the engine out of our 05 Envoy Denali because of some major knocking. Found the rod bearing gone, so time for a rebuild. LH6 Alum 5.3

Took the engine to Performance Engineering in Hamilton for the machine work. He got the rolling assembly, and that's how I got it back. So I put the heads, oil pump, timing cover, oil pan on. He did all the important stuff.
So the engine has a new crank, rings, and cam, plus all the rest of the usual wear items. I also removed the DOD crap.
Almost 3000 miles on the rebuild and my wife calls and says the oil light came on. The oil pressure on the dash was 41 cold and 35 warm at idle for 3000 miles. Now showing 22 at 3k rpms and 0 at idle warm.

I first thought the sensor was bad so i replaced it. No change.

Decided to pull the pan thinking pickup o ring or something in the pan. Checked all and replaced the o ring for kicks. No change.

Bought a mechanical gauge to make sure the pcm wasn't messing with me. Nope...

Next was the oil pump relief valve. Took it out and made sure it wasn't sticking. No change.

Next off comes the front cover to replace the cam retainer plate and the oil pump while it was open, again, just to be sure. All this was new already. and still no change.

Last was over filling the oil and raising up the rear end to see if it would change. Nope

Car runs great and makes no noise. I did notice and 10 psi difference in pressures between checking at the oil cooler port at the oil pan and the OE gauge location at the back of the intake. It was lower at the factory location on the intake.

So what would make it lose pressure besides the cam retainer plate, oil pump, and pickup o ring?