Cheapest and easiest check is the thermostat located by the water pump usually. Take it out and place in a bowl of boiling water. If it opens then that's not the problem. If it doesn't open entirely or at all then its probably the issue. I would start there.
If your gas gauge is not working on your 2000 Impala you need to take it in to a repair shop. There could be a fuse that needs to be replaced to prevent you from running out of gas.
Running the engine hot repeatedly.
alternator could have gone out running the battery dead.
A faulty sensor in the engine block.
dimmer switch wore out or you might just have running lights.
I had a problem with stalling with a 2000 Impala, and it was the oxygen sensor.
check the fueses check fueses
Engine running hot.
Impala HQ .com
2000 chevy impala sterio wireing color codes
where is the ac vacuum line on a 2000 impala ls> Yes I need to know about a LS
What are the torque specs for 2000 Chevy Impala 3.8 Litre ?