So far I have replaced the IVR with a new solid state one and replaced the sensor itself. As for testing the guage, I've grounded from the sender wire to the chassis and directly to the negative battery terminal, both giving the same results. The furthest I've gone for testing the sender wire was putting on lead on the sensor connector and the other lead on the guage wire within the instrument cluster connector, but made the mistake of only listening to the continuity beep function my multimeter has, I'll have to check for actual resistance.
