GE Freezer Model # FUM17DPARWH not cooling properly, I changed the Temperature Control, then it working better but not the best, it takes to long to freeze water or food

How clean are the condenser coils and does it have a condenser fan? It sounds like it is dirty. If the t-stat is not installed just right it will not work right. You have to expose only the length of cap tube as was the case in original and the rest coiled up behind t-stat.