Temp & fuel gauges - what am I overlooking?

Voltage is the same as it always had been - variable.

I keep testing and all I'm doing is convincing myself there's nothing wrong in the cluster.

I get an open reading checking the old temp sender. I probed the center stud and the body. Heating it didn't seem to have any effect.
Don't use teflon tape to seal the threads on the temp sending unit. Use pipe thread sealant.