When my ford f150 gets warm turns over slow or none when I shut it off

Hello, I am having an issue with my 1990 ford f150 5.8L larient. The truck starts up fine and runs but after a while the engine light comes on and the oil pressure gauge goes down to the low reading when at a stop sign. If I shut it off it will turn over slowly or not at all? If I let it cool down
it will start back up again very strong!!?? I checked the engine and does not seem to be overheating, no boiling antifreeze. The oil is clean and it has a new battery a new alternator and starter, so I am baffled? I would appreciate any response!!! Thanks Nick

I have solved this issue!!! It was a bad starter!!! Now it starts up great, even after it has been running awhile. Had a test done on the starter at a repair shop. It was drawing over 400 amps when warm, anything over 200 amps is bad. The old starter was only 1 year old from napa! Weird!