Dometic DM2852rbx Fridge/Freezer

I am having issues with my unit. The Freezer works just fine but the fridge just does not seem to get cold. I thought it was the thermistor so I unplugged it and the temps in the fridge would get cold -5 C in the morning. I replaced the thermistor with one of those snip the tip units and it seemed to work fine for a few days but once again the fridge is not very cold. I have unplugged the thermistor once again but the fridge no longer gets to that -5 range overnight. I have a new direct replacement thermistor which I could install but am not sure that is the problem. I am contemplating switching it to propane to see what kind of temps I will see. Could my electrical board be on it's way out? Looking for some advice as to what to look for here. Also what is the difference between the DM2852 and the RM2852 or is there any difference?