Fluctuating temp gauge

Other than checking for air in the system or bad fans, relays, low coolant level basically all the normal items and the thermostat. I would say bad head gasket. Do a compression check on all cylinders and/or test for exhaust in coolant if all the cooling system checks out.

You might try replacing the coolant temperature sender and thermostat to make certain they are not the problem.

Dose it do it when you turn a corner or come to a stop?

coolant temperature sender need to replace ,,,, as usual ... drama

Has nothing to do with gage thermast .It's in the wiring. Look on the passenger side of the truck.You will see the bundle of wires pinned to the fire wall around a line from the air conditioning. Pull the wires from the fire wall. Separate the wires . I have not had a bit of trouble since. By the way if you can get your local Chevy dealer to admit it, it's a problem they have known about for some time.

Would that bundle of wires Cause other electrical problems

The temperature gauge drop and make you about take off and get up speed it go back 210..