Because your stove, hot water tank and refrigerator all seem to work fine and ignite with the same propane (presumably
at your present 8100' altitude) it does not seem to me your gas regulator needs any adjustment. Read closely the specifications for your furnace to determine if it is equipped with an oxygen depletion sensor
. That is a safety device -- installed for your protection by those who dwell only at sea level -- which prevents appliances from operating when ambient oxygen is low. Unfortunately, it also prevents the appliance from operating at all above certain altitudes, which vary among manufacturers and devices, but seem generally to begin around 9000' above sea level.
I live in Denver, and when shopping for newer appliances for my vintage RVs I avoid buying any that have an oxygen deletion sensor because I want my appliances to operate at the high altitudes prevalent in Colorado.
If you furnace has an oxygen depletion sensor installed, that might be the cause of your problem. I don't know if they can be adjusted, but research that possibility if one is present. If your furnace does not have one installed, then you need not concern yourself about it and should continue to look for other reasons your furnace refuses to ignite. Maybe the air/fuel ratio needs to be adjusted; but then again with newer appliances perhaps that is controlled electronically and is incapable of being adjusted manually -- again for your safety . . . better frozen that dead.
Best wishes in getting your furnace to work. And Congratulations on your purchase and welcome to the wonderful world of Airstreams.