Why is my refrigerator over-cooling to the point of freezing?
This could be a bad Damper Control Assembly. Your fridge pulls cold air from the freezer section and more modern models tend to have an electronic controlled port that opens and closes to regulate the fridge temp. If the fridge is too warm or cold, the assembly is letting too much or too little in. 

That part is not terribly expensive (showing around $60 at various online retailers for your model) and seems to be easily replaced.