If the temp and oil gauges work, the IVR is fine.
Take the wire off the sending unit on the gas gauge and ground it. If the gauge pegs full, the sending unit in the tank is toast. If the gauge still reads E then go to the back of the gauge (easier to remove the drivers air box) and ground the fuel gauge there (sender wire, not the power off the IVR).
Gauge still read E when the others work? Gauge is toast.
Gauge suddenly starts working? Probably a bad gauge selector switch on the dash or a bad wire.
If you really want to try and read voltage on the sender wire at the tank (disconnected from the sender at the tank), it should be a blinking 12V with the key on.