97 lumina misfires when warm

I have a 97 Lumina with the 3.1 and 145,000 miles on it. Have a problem with a random misfire when warm or if you shut car off when warm does not want to start up. Have replaced the following already. Plugs, Wires, Timing Set, both crank sensors, cam sensor, throttle position sensor, EGR Valve, control module and all three coils. Car starts and runs fines when cold but once up to temp starts to misfire. If car is running at temp and you shut it off will not start again until it cools down. Code is P0300 random misfire. Have also done head gaskets and intake gasket as they were leaking. Fuel is good but have weak spark once car gets up to operating temp.

Coolant temperature sensor?

Check for fuel in the vacuum line going to the fuel pressure regulator. The presence of fuel/ fuel vapors would indicate a bad regulator causing it to run too rich when warm and cause hard starting after a warm soak.

Thanks for the ideas, just had neck surgery and as soon as I am able to get back on the car will check both of these options out.