IVR pulse at 4 volts gauges read low

Well if you have an o-scope, then use that to look directly at the voltage at any of the wires to the sensors. The 'ideal' duty cycle is around 17-18% with an input of 12v. (Contrary to the info on Allpar.com) At 14v, the pulse % may be a bit lower. The pulse rate of 1 second or more sounds fairly normal.

The way this IVR works, is that when power is applied, it sends 12v through to the gauge circuits, and at the same time, applies 12v to a nichrome heating wire in the unit. This heats and bends a bimetallic arm, and when this bends enough, is opens a contact at the input; that removes the 12v from the heating element and the gauge circuits. When this cools, the contact closes and 12v is applied again to everything and the cycle starts over.

The duty cycle is set at around 17% so that the RMS voltage (not the average voltage) to the gauge circuits is 5v. If your IVR is short cycling, then the duty cycle will be around 11% if the RMS voltage it is sending to the gauges is 4v. (But I don't think your 4v analog meter readings are giving you the true story.)