It is unusual that they flat die with no warning, but it happens.
Just start checking everything from the basics, check the oil, check the coolant, load test the battery, All grounds, return line from the IP. Juice at the PMD connector - you can find some diagnostic links on a thread I started on the 94 a couple years ago in December. My 94 quit like that. It was a wire in a connector that lost contact after many years of being plugged in. Took me forever to find it.
I had another truck quit like that - it was the injection pump return line plugged. A shot from the blower on the air compressor and it ran great.
I also recommend to get a new engine wiring harness. Ours are all getting old, brittle and crappy. Kind of like me - except the crappy part. Well maybe that too.
It's just something I have started changing as I work on vehicles.
I had to many little issues here and there. Broken connectors, brittle wires and such. I got to thinking I wouldn't run on 20 year old tires because of old rubber / plastic. Maybe it's not a good idea to run on 20 year old wiring. It's not like GM over sized the wires or anything