Losing engine gauges, speedo, and fan staying on

[Colter]

It should be communication issue between ECM and CAB. Low voltage at the power pin in the 9PIN or the J1939 voltage?
If you have ESA you can connect to CECU and check for any code listing a CAN line failure. These issues are usually outside the cab under the hood, I would start by finding the blue resistor plug in the OEM harness along the drivers side of the valve cover. It'll have blue/yellow wire pair in and out of it. There may be a loose pin or a rub somewhere in that wiring.
Peterbilt also tend to get rubs in the ECM power supply but the symptoms don't really match that, I'd assume your hours and KM go to dash's when the issue happens as well?