Temp Gauge Issues

If the IVR is the original type I'd get a solid state replacement. ALSO the contacts where the IVR plugs in can get corroded and you must solder across them to bridge to the PC board traces. Check the connector pins for loose, and repair. Last the nuts on the gauge nuts need to be loosened/ tightened to "scrub" them clean

There's an old thread on this and it's a good one

Printed circuit pins repair