2001 Silverado 1500: volt gage fluctuates

[biketopia]

odd are it's the gauge (stepper) motor. They do fail and or get sporadic, usually it's the tach or speedo put all of them are known to have issues since it's the same motor. There's companies online that will refurb your dash or you can do it your self. There's lots of how-to info online and the motors are cheap enough on ebay or amazon. If you have a scan tool that can monitor some data like voltage that will tell you what the ECU and seeing and if it's staying steady and the gauge is moving around that's a pretty solid confirmation your gauge motor is on it's way out