I have a 1997 Pontiac Sunfire with the 2.4l LD9 and 4T40E auto trans, 195k miles. New water pump, hoses, thermostat, radiator within the last 20k miles. New plugs and OEM coils around that same time. My issue is in very hot weather or stop and go traffic the engine temps will climb, within safe levels, but then the engine will develop a misfire at any speed/rpm. This only occurs when the temp gauge rises above center, but still quite a ways from yellow. I have slight coolant loss due to unidentified leaks but head gasket is okay. Turning heater to full blast to cool car back down fixes it. Any ideas as to what could be causing this? No relevant CEL.