AT this point both gauges are most likely bad, it is very hard on a gauge to leave it "pegged." If you could remove your 4th pod & send it to me (the whole pod) I would be happy to test them for you. Gauges need to be wired to a sender, espically the oil pressure gauge. If not it tries to go beyond full scale,, this puts the gauge into a bind and can throw the calibration off. I have repair and/or replacement parts to fix any gauge out of any year GTO.

Pete