IVR pulse at 4 volts gauges read low

Wow; a zillion responses. Here is my final input. If your IVR is bad and the instruments are, in fact, reading low, you will have to pull the instrument cluster regardless. You will either have to pull the gas gauge to have the built in IVR fixed, or to bypass the gas gauge IVR with a digital one (remember the link to D&M). I see no way to fix your problem without pulling the instrument panel.