My GE fridge/freezer is having problems. The Freezer temperature jumps around all over the place, while the fridge stays normal and on-temp.

The temperature on the freezer - if set to 0 degF - varies from below zero to up into the 20s. Doesn't seem to have any direct relation to how often the fridge opens or closes or anything - could open the fridge in the morning after it has all been closed for 8 hours and the freezer will read 14 degrees (or whatever) while the fridge is right at 37 where it is set.

I have not put a thermometer in the freezer - don't have one that reads that range - but based on the melting of the ice and frosting up of stuff inside, I think that the temperature reading is generally accurately displaying the temperature in the freezer - it's not cooling properly, rather than cooling properly and reading wrong.

What are my next steps for diagnostics and/or recommendations for replacing parts to fix the issue?

Thanks in advance.