I cannot get the refrigerator to go less that 50 degrees?

Wow! You’ve replaced almost every part. This is either a problem with air flow or refrigerant . You’ll need to unplug refrigerator and remove the panel inside the freezer to expose the evaporator coils. If the evap coils have ice built up all over them, the problem is in the defrost circuit. If there is ice on part of the coils, there’s a problem in the sealed system. Where the refrigerant lines come through the wall at the evaporator, if you notice a clump of ice on the tubing near the wall then you have a sealed system problem. The coils should have no ice

Next you need to take the rear panel off to access the condenser fan motor then plug in the refer. You need to watch the evap coils you’ll hear the compressor turn on and both fams should be running while compressor is running . Watch the evaporator coils and time how long it takes for all the evap coils to have frost on them. If it’s longer than 10 min that’s a seal system problem. If all the evap coils have an even frost pattern all over them within a few minutes, than the sealed system is fine. Next, check the evap fan blade is turning proper Check for air loss through torn or damaged door gaskets. If all is fine then shut the doors and allow 48 hrs for the refer reaches set temperature.

I’m curious to know if you ran a vscum on the system befor you charged and for how long. How much refrigerant did you add and did you repair the leak.?