If your rig is on a Freightliner chassis, it should have a VDC (vehicle data computer). The VDC collects engine and transmission data, converts it to digital and sends it along on a data bus to your gauges on the dash.
If one or more of your gauges are acting up and its not ground related, then I would suspect the VDC. There are other posts on this forum for the VDC repair procedures if you are comfortable with a soldering iron.
The Freightliner Help Desk at 800-385-4357 can help diagnose problems, have your VIN# ready.
Denny, Connie & Shadow (former barn cat made good)
2000 Itasca Horizon, Cat 3126B, Freightliner Chassis