Is this a 302 or 2.3 engine?
There are a couple things I would check first. The ignition switch is #1. Just remove the plastics on the lower steering column and inspect it. If there's any signs the plastic side is separating from the metal side, replace it.
Presuming it's a v8 car, check the tfi module on the distributor. The parts stores sell a handy little tool for removing them. Well worth a few bucks. Remove the module and take it in to the store. Most parts stores can bench test them. If it tests good, have them repeat it a few times. They will often fail once they heat up.
Another thing to check is your fuel tank. When you replaced the pump, did you get a good look inside? My 88 had some rust in the tank. After driving for a few minutes, the sock strainer on the pickup tube would clog. After the engine was stopped for a few minutes, enough of the sediment would drop off and I could restart it.
Check grounds, as well. Specifically the ground strap from engine to firewall, another smaller ground wire from the fuel injector harness to firewall (orange wire iirc) and a blue wire ground near the battery (can't recall what that one is for).
Clean your tab/tad connectors (aka salt & pepper shakers). Check wiring on your fender-mounted starter relay, check main battery connections, and check your fusable links near the starter relay. All are common problem areas.
If all else fails, you may find that you're ecm is faulty. There are 3 capacitors that go bad and need replaced. Very cheap to fix if you can do it...a little more if you pay an expert. There are some YouTube videos on it.
That should at least keep you busy for a while lol! Let us know what you find out.
