Malibu '97 Indmar

I have a '97 Malibu Sunsetter with an electronic fuel injection system. Runs great with the exception that after it has warmed up it will lose power after running for about 15 min. If I turn it off and back on it will run great and repeat the same thing after about 15 min. We have replaced the injectors, fuel pump, distributor cap and plug wires. It is still having the same issue. Not sure if there is a sensor that is shutting the engine off or starving the fuel line but I am at a loss as to what is causing this. No change in engine temp. Oil pressure seems to be fine.