Are you not having any problems on steep grades if you keep moving (climbing a long hill)? I don't know what you have looked at yet, so, I will tell you what comes to mind.
You might have some water in the fuel (low fuel level will aggravate this because it will move around more).
If it dies while you are holding the brake, check your vacuum booster. may be a bad diaphragm. either disconnect the booster and plug the line, or park it on level ground and press the brake HARD while it is idling. see if it dies. Or, stop on a decline and set the e-brake quickly and let off the brake. If it still dies, then the booster is not the problem, and i would look for loose or shorting sensor wiring/plugs.
Also, check your idle speed, and the adjustment of your TPS. When it is searching for an idle, did it sound like the ignition was shutting off, then coming back on, repeatedly? If so, i would definitely check the tps.
That's all I can think of off the top of my head. If you have time to study, look through the fsm diagnostics: http://personal.utulsa.edu/~nathan-buchanan/93fsm/