Fuel and oil gauges pegging

Is the IVR electronic or mehanical?

Iirc the Ivr is imbedded on your fuel gauge

I did not understand the temp gauge does it do the same?

Technically the gauge cluster is grounded by the screws that hold the dash to the car

But that would be a quick check. To see that you have 0 or near 0 ohms between the metal of the cluster and the car body

I am in the middle of the same thing. 67 dart. But in my case I know it is the OEM IVR. And am waiting on my RT-Engineering replacement to see how bad the temp / fuel gauge/s is/are fried.