The freezer unit gets the "cooling" first. If inadequate, there is not enough left to absorb the heat in the refrigerator.
Many factors can limit cooling-- these are some of those related to the LP heat source:
Low propane pressure (regulator may need adjustment or replacement
Dirt in refrigerator gas jet
Dirt, rust or insect nest in burner tube
Basically, start by doing a COMPLETE burner area tune-up, not a short cut "blow it out" one.
Check propane pressure to insure it is 11" WC.