After doing a little research online I came to the conclusion that it was probably the defrost timer or the thermostat, and after watching a couple installation videos on AppliancePartsPros.com I felt confident I could do the repair myself. I ordered both parts and they arrived quickly and installation of both parts only took me about 30 minutes. Unfortunately, my problem still existed and I was back on the internet for more research. This time I found that maybe it was the defrost heater bar that needed to replaced. Again, AppliancePartsPros.com had a very helpful installation video and I proceeded to order the defrost heater. Again, quick delivery and another 30 minutes of my time and the installation was complete....this time I had success! My freezer was ice cold and there was no longer a ton of frost and ice build up, and my fridge was getting the cold air it needed to work properly. I considered uninstalling the other two parts I ordered and returning them but I figured, what the heck...now I don't have to worry about those parts for a long time either. Very easy repair, very good price for the new parts, quick delivery. I'm very happy!