1995 Buick Riviera S/C Intermittent Stalling while idling

Engine Performance problem
1995 Buick Riviera 6 cyl Front Wheel Drive Automatic

Hello all. I've got a 1995 Buick Riviera S/C with a rather annoying engine problem. I've got ~151,000 miles on the car, and have:

Replaced the S/C, and all pulleys and belts.
CAM Sensor
Crank Sensor
EGR Valve
3 Coil Packs
and Fuel Filter.

Sporadically out of nowhere, the car will stall while idling stopped at a traffic light. Sometimes it will refire immediately, others it takes about a minute or two.

I have noticed occasionally when driving that the PRND321 light will flash and all interior gauges will reset, and once in a while the Outside Temperature on the heater control will flash.

Sometimes, from a cold start if I overrev the accelerator, the car will just sputter and stall -- also sometimes when cold cranking, it will sound like the car "backfires" and then starts.

Also, the ABS light constantly stays on (but I doubt that has anything to do with this problem).

I'd like to just push the car into the river but I've gone too deep into my pocket already to just get rid of it. Hopefully it's an easy fix, but I'm not so sure. No mechanic can seem to get it right, so I've turned to the internet! Thanks for any and all help!