In the process of figuring out what is going on with the refrigerator in my 2004 17' Towlite, I have been consulting a number of different manuals, (can't find the specific one for my refrigerator) but all of those manuals are addressing your issue.
It is not unusual for the outside temp to affect the temp inside the refrigerator and above 80 deg F, the refrigerator does not work all that well without some boost to the ventilation for the coils in the back. So, having lived in Laramie, WY, I am sure you're having quite cool nights, greatly increasing the ability of the refrigerator to cast off the heat, but in the day, not so cool, so the change to 45 deg is not a clear sign that there is something wrong with the unit. 45 deg is a good fridge temp, I'd be happy with that temp here in not-so-cool central Florida.
The second point that might apply to some of your outings is that above 5500 feet Dometic says to not use the propane to run the refrigerator as the elevation change affects the efficiency of the burn. I suppose this is something like the change in cooking instructions above a certain elevation. I doubt this is the cause of your current problem, but I thought I would mention it as I was surprised to see it and will have to remember that myself when I eventually get out to the mountain west.