Are you still under warranty? If so, have the dealer replace the fuel sender unit which is attached to the fuel pump in the tank. That is the usual cause. If you wish, you can try the GM fuel additive which is designed to clean the contacts on the sender. As far as I can recall, we haven't had any report back that it has fixed that problem. If you are not under warranty, and are good at working on things, there is a cheap fix that has been posted for that problem.
Is the car no longer overheating? Have you checked your coolant level, both in the overflow tank, and the radiator? This is a techinfo article that you should be aware of.
Black 2000 SSEi, Silverstar Headlights, Angel Eyes fogs, 3rd brake light overlay, hi-flo cat, drilled 180 degree thermostat, Intense FWI, PCM, shift kit, and 3.4 Pulley. Solid front mount.