Your motorhome has a vehicle data computer that collects info from the engine computer and the transmission computer, and forwards that info along a data bus to the light bar unit on the dash. There is a spider harness from the light bar unit to the individual gauges. All gauges get all of the info, and each gauge is designed to get what it needs from the information flow.
The first step is to swap the leads between working gauges and the inoperative gauges to see if the problem is resolved.
Use the link below to download Freightliner SB 54-12. It describes how your instruments work, and the related troubleshooting.
You can also call the free Freightliner Help Desk. Have your vehicle VIN number (last 6 digits) available as they will ask for that information. 1 800 FTL-HELP
Most likely you have a dirty connection to the gauge itself, or a connector on the wiring harness that is dirty or loose.
I had my speedometer spin down to zero once while traveling at highway speed. After the next stop, it started working again and has not failed again.