It sounds like you may have to do a few things to sort out your problem.
First, remove the kick plate vent at the bottom of your fridge. It may be blocked with lint, pet hair, etc. and causing the compresser to work harder than necessary.
Second, carefully vacuum underneath and beside your fridge and if possible, from behind as well, being careful not to rupture the connection for your icemaker.
Third, check the settings dial for BOTH the fridge and freezer segments of the appliance. If they are set too cold and if the freezer has an ice buildup over the venting area, it can make the compresser overheat or work overtime causing uneven cooling.
Fourth, check the seal of the door. If there are gaps or areas that are compressed, the cool air will leak from those areas forcing the unit to work overtime to compensate and freeze items in the back of the fridge.
If all of that has been done and you are still experiencing uneven temperatures, call a repair service to check the level of coolant and to examine your unit for leakage or issues with the thermostatic regulator. It may need to be replaced or repaired while not having to replace the fridge itself.