When the problem occurs, have a helper crank it, while you visually check for spark at the plugs. If that check out, use a gage and check fuel pressure. Some of the national brand autostores used to loan out a fuel pressure gage, if you don't have one. Don't let gas spray all over a hot engine. Safety is your responsibility.
To check for spark, you can use a known good spark plug or spark tester, carry it in the glove box, it won't get hot. If the engine is hot, wear gloves and/or use a spark plug wire puller. Pull the plug wire, stick tester in the boot, ground metal part of plug/tester to metal part of engine. Engine cranking, watch for spark. Let us know what you find.