I also have a 2016 model with a Norcold refrigerator. I see you are from the West. Depending on the elevation you may experience cooling issues. Norcold states in the manual the refrigerator should be operated on electricity above 5500 ft. I have operated above that on propane and noticed some deterioration in performance. I think there is a good bit of variability from unit to unit on how they perform at higher elevations. Since you say it operates ok on electricity but not propane it basically has to be due to inadequate heat being delivered by the propane. Obviously there are several things that can cause that but it appears you have already addressed the major ones.
You said you had cleaned the burner tube, if you haven’t already you should carefully clean the burner jet as well. A proper clean flame is important at any elevation but especially so at higher elevations. Proper gas regulator pressure potentially could also be a contributor as well. This should also be checked.
If your inadequate cooling is indeed related to elevation then this is another disadvantage of of a propane absorption cycle refrigerator when compared to a 12 volt compressor style unit.
Thank you!! I appreciate your advice. My elevation here in Montana is 2380. Don't feel that should be a issue. I also seem to have a very clean flame. ?? I don't know if i should just buy a new refrigerator. Not sure about how to physically change it??