The freezer is frosted up and defrosting. It defrosts when using forced defrost. Refrigerator is is not cooling. The thermostat kit was replaced and for a while it worked fine. Now its back to the same problem.
Here are your parts
http://www.appliancepartspros.com/parts-for-whirlpool-gb2shtxtb00.html
The freezer is frosted up and defrosting.
Sorry but I found your post confusing, "frosted up" and "defrosting" are opposites.
If the problem is that you can force a defrost cycle and the unit does defrost but heavily frosts up again over a few days then I would say that the control board needs replacing as it is not automatically starting/programming a defrost cycle.
The board is Item 5 in the Refrigerator Liner Parts section. Click on the picture for more info on it re: a Q&A section etc.