No question about you having a problem. There have also been other posts about the same problem. However, There are lots of RVs out there that don't have the problem. We live at 5000 ft and no problem and we travel to higher elevations with no problem. Several years ago I had a similar problem. Some appliances worked others wouldn't. Turned out to be a regulator problem. Regulators are cheap but I wanted to find out what the problem was. They checked my regulator. It wouldn't furnish the proper pressure and ajustment was erratic. Propane dealer said sometimes dirt gets into the regulators from dirty propane. Not different from getting dirty fuel in our vehicles. It becomes a PITA for us.
BTW: I had taken my gas range in for an RV dealer to repair. I was really upset when it still didn't work after I paid the bill. I lost my temper with the guy. After finding out it was the regulator it was embarrasing but I had to go back to the RV dealer and apoligize.