Temp Gauge Working Intermittently - Suggestions?

If you pull the cluster you should go "clear through" it, generally

PC connector pins can be loose, and can be fixed by soldering

IVR connctor is spring loaded contacts pressed into the board. Solder bridges across them to the PC board traces

Already mentioned the gauge nuts

Replace IVR with a solid state one like RTE

Use eraser, etc, to clean up the traces where the lamp sockets fit, and bend the socket tabs for better contact