I had exactly the same problem on our Bus, except I was in the woods in Alaska. Recovery within a few seconds and it didn't happen for another 10 seconds or an hour plus. When it finally quit long enough for the brake pressure indicator to go to zero and stay there for about 10 seconds, I knew it was an indication rather than air problem. (My emergency brake should have set and it didn't)
All the gauges on the front dash, including the speed and tach are on a single wire. The computer in the rear takes all the necessary readings and streams this info as a code and a reading on a single wire to the dash. This is called multiplexing. All the dash readings are on this same single wire, daisy chained one to the next. If you have the oil pressure first on the wire, you can pull it and put it last on the wire and it'll still show the correct reading.
What I did to solve my problem was to simply pull all the wires and scramble the order they were hooked up in. Since I did that, I've never had my problem again. This could be a simple and cheap thing to try that might work. Good luck.
2013 Tiffin Allegro Bus 43QGP
2011 Chevy Silverado 1500 Toad