GE PFS22MISBWW Refrigerator starting fluctuating its temperature. I first noticed it in the freezer as items were melting and refreezing. The refrigerator also heats up. For periods of time throughout the day it works perfectly then at some point the temperature rises above the set temperatures. The fans all run, the compressor kicks on, and everything is fairly clean. I first replaced the three thermistors. No change. I then replaced the main board. No change. I then replaced the run capacitor. No change. It seems to me that something is keeping the defrost heater on too long. The only other item I can see that might help is the defrost thermostat, but I thought that was more of a failsafe in case it gets too hot rather than part of normal operation. Does anyone have any other ideas or should I just try the thermostat?