68 Barracuda........ Temp and Gas Gauge Issue.

Your temp sensor readings make sense for the resistances and temps you recorded.

To make a crude check of the IVR in the gauge, pull the wire off of the temp sensor, turn the key to RUN, and look at the voltage coming out of the temp sensor wire. It should be pulsing from 0 to some + voltage. If this voltage is always 0 or 12, then it is bad. 'splains why the 5v regulator was put in at one time.

IIRC, the connection to the temp gauge from the IVR is on the circuit board.