Fluctuating Idle '90 GP

1990 GP STE
200,000 mi or so
V6 3.1L

When my car is running, the engine idle fluctuates/flutters. It revs up and down a 50-100 RPMs, and when it's in gear, the car will rock forward every time they go up. It's really annoying and I'm sure it's not good for my engine.
Just got all 6 fuel injectors replaced (to the tune of $500), and the problem remains (but the injectors were replaced because the car kept stalling and they were mostly shot). New wires/batt/alternator as well. I really want this fixed. Also, the oil pressure guage fluctuates. I think this may have something to do with it. Do I have a bad vacuum seal or something?

I'm planning a road trip soon, so any advice is greatly appreciated.

Thanks
Sam

I would clean the following items, the idle air control motor. Located on the side of the throttle body. The mass air flow sensor. Will get dirty and cause the car to search for idle or idle very fast. Use throttle body cleaner on the IAC motor and make sure it is dry before you put it back in. Use electronics cleaner on the MAF sensor. Both are available at most autoparts stores.