Just the other day i noticed my tank was reading full, way full after a long trip. It was obvious that the tank was no longer full so i believe the system is grounded out somewhere along the way. i dropped the tank to replace the fuel sock on the pump and as well test the gas gauge sensor, which worked fine according to my voltmeter. couldnt find any breaks in the wire. has anyone experienced a failure of the gauge in the dash cluster?

 

In my 85 Iroc, the guage quite often reads full until it drops to under half a tank. You may have the same issue