What type of freezer is it, walk in, reach in, or undercounter?
OK. Thank you. As a rule, refrigerators and freezers are reliable appliances. When problems arise, they're usually caused by condition outside the sealed system and its control circuitry.
If you have'nt already done it, check the surface of the condenser coil for a dust layer blocking the air flow through it. Vacuum any you find with a ShopVac. Check also to make sure the condenser air fan is clean and working properly. Dust and grease buildup on the fan blade will reduce air flow. Lastly, check for ice buildup on the evaporator coils.
All these conditions will reduce the units cooling capacity. In my opinion, the advice about needing a stronger compressor is erroneous. The original compressors are well designed, and have plenty of cooling capacity.