Top thawing, bottom frozen, freezer is only 5 years old, only paid $450 for it new

You are having a problem with the defrost system or fan. I would bet it is the terminator opening too soon if it's defrosting at all. Thaw it out and remove the cover to freezer coils and check the element with an ohm meter after unplugging it. Also, check under unit and clean the coils very well. You will have to remove rear cover to do this and the front kick plate cover. I always blow it out first then use a water hose and spray the coils briefly to get the rest of the dirt off. Clean off fan blades, too. Replace cover. Let me know what happens. DrTom4444