My kitchenaid side by sude freezer drops to -10?

My freezer gets too cold. Compressor seems to run most of the time. I have replaced bi-metal defrost, defrost heater element, both control boards, both fans, two thermistors,, and the damper between the freezer and fridge seems to operate correctly. It will appear to work okay for a little while, then drop down to minus ten. If I let it go, eventually it goes back to proper temperature. A few hours later... back to minus 10. I have just been letting it go at this point. Wondering if I got a bad refurbished main control board. Any ideas???