65 Valiant now gauges go full when ignition key turned or running

OK, well first test the voltage at the lead at the temp sensor as I described to check the RTE IVR. It is supposed to mimic the original IVR and should show you a pulsed voltage; your meter will show it jumping up and down.

Then test the gauges with some resistors like Del says above. They can be small resistors but they might get hot fast. I'd try one around 22 or 24 ohms connected to the end of the temp sensor wire to ground to see if the temp gauge went to near mid-scale.

Do you have a PN on the temp sensor? The new ones tend to be off from the originals. And take a resistance reading through the temp sensor with the engine warmed up (if you can with the trans leak) and let us know.

And BTW, this sensor uses a temp sensor, not a temp switch; those are distinctly different parts.