1990 Chevy cavalier gets hot and shuts off have to let it cool for a few hrs before it will start again Have replaced oxygen sensor tune up computer thermostat flushed radiator and car still same?

It very well could be your fan not turning on. There is a switch that tells it to turn on. I think its a temperature sensor in the coolant line. Start it with the hood open. Once it gets about 200 degrees the fan should turn on. If it doesn't, bad sensor/switch. I have seen some people hook the fan up to a switch inside their car haha. I would say that it is the fuel pressure regulater. When they go bad they affect the car only once warm. It is located on the top back side of the throttle body. If you can check the fuel pressure at the fuel rail the pressure should stay the same after you shut the car off. If the pressure goes down after you shut off the car it means the fuel pressure regulater diafram is leaking(bad).