Notice

NOTICE: Please anticipate up to a 5 business day turn-around on repairs after we have received your unit in for service

Faulty sender units are common to some GM vehicles, but generally speaking will start malfunction at the same fuel level every time due to wear at the sender grid.
Also, you may get a fault trouble code which is usually an indication of a faulty sender or circuit.
A malfunctioning gauge esp. on some GM vehicles will be stuck and not move at all or be off the scale altogether.