Freezer runs for about 1 day before my GFCI gets tripped. I checked and there is no loose ground wire so I am suspecting defrost timer or defrost circuit is shorting out. If I plug it into non-GFCI circuit, nothing happens.

When this happens, if I unplug it for about 3-5 hours and then plug it back in, it works just fine for another day or so. (about 12 hours to 20 hours)

There is possibility that overload protection is kicking in as well.

What would be the best method to test the defrost timer?

IF it is defrost timer, then why would it work when I unplug it for few hours but not right away (GFCI trips right away if I reset the GFCI)? the timer will be stuck at defrost setting while it is unplugged, no?

This is pretty much the first appliance repair work that I am doing. I have done some electrical work - wires, switches, etc. and actually computer programmer by trade. Now, IF it is starter/relay part, is there possibility of replacing the separate starter/relay/overload with 3 in 1 relay combo kit?
(In this unit, the parts are 5303206816 - Overload, 216008900 - starter, 5304464438 - run capacitor, totals about $100 where as 3 in 1 is only about $28 - AP3540659 )

When it runs, it seems to run normally - gets really cold, temperature is steady, and everything seems normal.