OK, too soon to declare victory, but the car does run and accelerates normally now. Hopefully that is not a fluke!
So, some answers:
1) Yes, any of the models above exchange the same PCM as the 95 Riviera.
2) Yes, it is simply a plug-and-play change, just swapping over the PROM. No programming/reprogramming required.
3) It is literally a 10 minute job of removing two screws to drop the under dash panel, unplug the three color coded harnesses, move the plastic clips to the side, and the PCM just slides out, maybe 15 if you take your time. Of course one should disconnect the battery during this process.
4) Reverse process to reinstall (after swapping the blue PROM from inside the case)
So, some interesting discoveries.
I pulled two PCM's from the yard, one from a Lesabre and one from a Bonneville. Both turned out to be remanufactured units. When I pulled the PCM from the Riviera, guess what... it too was remanufactured.
After doing a little more Googling and reading about this series PCM, it seems that the 95 units (and probably the 94 too) are failing relatively commonly. And based on my discovery of 3 for 3 being reman units, I would tend to agree.
That leads one to wonder why. Who knows. But it is also interesting that there are so many reman units available, and affordable. I doubt they are replacing ICs, but instead are probably replacing something like a capactor(s), resistor or cold solder work and that stuff is cheap.
So I'm going to tear apart my 'broken' one and see what I find. It would be interesting to discover that these are failing due to something as simple as that. It could also be a transistor, which is harder to detect to some degree of course. But I bet it's something like that.
Anyway, if your 95 starts going wacky in an odd way with no or weird codes that the seemingly appropriate repairs don't address... the PCM may be the issue. I'd get a cheap one from a yard for $30-50 and see if that clears it up.
We'll have to drive it for a week or two before I'm convinced of course, but so far it seems to be acting more normal than it has for a long while.