Start by getting yourself a cheaper spark tester, auto parts store, Harbor Frieght, etc. Then the next time it happens see if you have good spark on each cylinder. In my opinion there are normally four things which will cause this problem. A coil which has a hot short or open when it gets hot. Vapor locking when it gets hot. Head gasket going bad one one or both cylinders when it gets hot. Valve clearance changes when it gets hot. We will need to start somewhere to eliminate the cause one at a time, not jumping around. Don’t assume anything can be eliminated until you have tested it and proved it is not your problem. Finally when you post back, make sure you include all engine numbers so we know what you are working on.
PS: Delete your other thread, no need for two, as it can get very confusing if different members are posting on different threads dealing with the same problem.