Strange issues with '94 Ciera S-3.1L V6 VIN M

I have been having some strange issues with my car lately. First off, I have the rear speakers amplified and I can't seem to get rid of a buzzing sound in those speakers when the car is running (pitch increases with speed, so the noise is probably the alternator winding up). I have had the alternator, which isn't old (new as of a year or two), tested a few months ago at a checker auto nearby and the battery tested last weekend. I was curious about both of them because on two separate occasions, I was waiting for a left turn arrow at night and all the lights dimmed and the idle became very strange. As I accelerated after the turn, I heard a loud squeak once or twice from the passenger side of the engine compartment. It turns out that the alternator is, as I hoped, excellent and the battery came back 100%. I turned as much on as possible, and pushed the accelerator pedal down for him and it came back good.

Well, the idle has been rough, possibly misfiring but i'm not really sure. I made sure the battery connections are tight after the second incident, just to be sure. On my way back from a trip to a nearby city this afternoon, I was turning onto a residential street listening to some music (didn't have it up very loud, though) when I noticed that I wasn't accelerating anymore as I neared the turn. To my surprise, the engine stopped running when I was driving so I turned the music off, pushed that break pedal down hard and cranked the wheel over very hard and stopped about 10 ft down the street from that turn. It really didn't crank over very well the first try, so I turned it off and then it cranked over really quickly.

It periodically would stall out when I sit at a light before we discovered that the fuel pump was faulty about a year ago, and that hasn't happened since. We have also replaced, in the span of the last 2-3 years: the MAF sensor, spark plugs, plug wires, coolant sensor, PCV valve, neutral safety switch (we had some transmission troubles in October) and throttle position sensor. We've been doing good, regular maintenance on it and recently replaced the completely worn down shocks and struts (replaced the ball joints too, for good measure), which definitely made a world of a difference.

One thing that I know for certain we have never, ever touched are the ignition coils or the crankshaft position sensor. After a local transmission shop was doing a road test to make sure everything was okay, he said the EGR Valve kept showing up on his tester that he had connected to it but I never did anything about that. I was thinking of having checker or autozone see if there are any trouble codes set tomorrow afternoon, too. Does anyone have any ideas? It seems to be getting gradually worse, especially now that it has actually stalled out on me while I was driving it, so I wanted to see if anyone has any ideas. Other that the issue mentioned, it is otherwise rock solid and doesn't seem to have problems. Before this issue, it idled so smoothly that you wouldn't even know it was running. Now, it sounds like its idling decently but you can definitely feel a shake in there that wasn't present before.

Thanks for any advice, opinions or help anyone can provide. It is greatly appreciated!