Kitchenaid freezer will not stay frozen 5 years...

Question

I have a kitchenaid side by side refrigerator (frost free) 4-5 years old, no longer under warranty. About a week or so ago the freezer stopped freezing, the refigerator seemed fine. So I turned the freezer temp control up a notch and when everything was frozen again I turned temp back down to normal. It was fine for another 3-4 days then it happened again. I pulled the grate off bottom and cleaned off the coils they had quite a bit of dust on them. Plugged it back in at normal temp and still wasn't freezing so I turned up a notch again then it froze but only lasted a day. This morning it was defrosting again. Do you have any idea what would cause this.