I'm looking at picking up a 2nd gen with a 3.1. Owner says it starts, runs and dies after about 20 min or running. Says it sits for another 20 min and it will start again.

What are the thoughts on what this may be?

I've had a '93 that did similar and I ended up needing coil packs. (That car had many electrical gremlins).

I wonky fuel pump could in theory do similar, altho how consistent it is makes this less likely (but not impossible)

Just looking to get everyone's thoughts on this.

Hello
Those symptoms are likely from the ICM. They'll over heat and fail (thermal paste deteriorates over the years). Once it cools down some, it will run fine again for a bit. Repeat cycle.
You should remove it and have it tested. If it test out okay, just get a tube of Super Lube Silicone Heat Sink Compound 98003; https://www.lowes.com/pd/Super-Lube-3-oz-Tube-Silicone-Heat-Sink-Compound/5001657135
Make sure you get this exact tube. They make other stuff in tubes very similar looking. You want the 98003. You might find it cheaper, it certainly used to be a few bucks less.

Most likely that is all it needs, based on what you described. I'm not ruling out fuel injectors. I'd just look at the ICM first thing.
Good luck.

Does it:
(A) run perfectly for 20 minutes until it suddenly stops? OR...
(B) start to run rough after 20 minutes and then stall out?

If it's B, then it could be a failed coolant temperature sensor (not to be confused with the thermostat). If the coolant temperature sensor fails, it can tell the computer that the engine is cold when the engine is actually hot. So the computer sends a too-rich fuel-mixture and the engine starts to run rough and stall out after it warms up. (It's the equivalent of keeping the choke on in an old-style engine.)

If it's A, then I have no idea.