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Misfires ECU Temp

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I have a problem that I have been chasing for a while and I can not figure out what is going on. Mazda 323 GTX BPT Turbo 1.8 G4+ PNP. When the car is stone cold and runs until normal operating temp everything runs fine. After a while like 30-35 minutes running the car pushing different loads (boosting and cruising) more or less the car starts to misfire even at light load. I changed everything ignition related (coil, cap and rotor, module, new leads, spark plugs). Besides a new set of DW 450cc high impedance injectors the engine is completely stock.
Compression is good 170psi all 4 cylinders so the engine is healthy. Now I noticed something. When I shut down the car for a while for 10 to 15 minutes and look at the ECU temp is around 100 degrees Fahrenheit . When I start the car again and drive it the misfire is gone. But when the ECU reaches about 115 degrees the misfires start under boost. When it reaches 120 to 125 degrees the misfires get worse even at light load. Again I shut down the car (engine still hot) to bring down the ECU temp to 100 degrees, start it over and the misfire is gone.
So I am getting suspicious that the ECU drivers for the injectors and ignition are having problems (overheating maybe) and because of that the misfires. The ECU is in the stock location.
Please advice.
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