Hello I am having some problems with my car, mostly in how it is running. Here's what I'm driving:

1989 Firebird Formula 350 Auto
5.7 L L31 Vortec
Scoggin Dickey lower intake manifold
24lb Bosch III injectors
Southbay Adjustable Fuel Pressure Regulator
charcoal cannister, smog pump, and EGR removed
everything else is stock (as far as Ive found) or replacement parts I've bought

AFPR has not been fully set up yet, pretty sure the pressure gauge is crap. Going to get to that soon, but all the conditions below were present before removing the stock regulator.

Bought it without a motor, installed the engine and got it running earlier this year. Always has had problems running. Idle was very erratic initially and didn't run too well. Replacing the injectors and changing base timing helped steady out the idle quality.

1. Biggest problem remaining is that it runs worse once it has been running continually. Eventually idle drops to 500rpm and then you can feel it struggling and then it dies. It starts back up with no problem but still dies occasionally when at a standstill. I believe that it gets bad once it reaches operating temp and goes into closed loop running. Is that realistic?

2. Oil pressure is just above 30 when car starts, gradually drops down as it warms up. The engine doesn't sound like its dying, does that point toward a bad sensor/gauge or bad bearings?

3. Car runs really rich and gas comes out of the exhaust. This points toward the air/fuel ratio set by the fuel pressure, and/or the O2 sensor right? Planning to mess with both of those, anything else it could be?

Thanks in advance for any help and advice