My 2000 Grand Prix GTP Supercharged was running fine but it shut off with a "check guages" warning. The gusges were fine and the car will start but it shuts off right away. The engine will stay running if it is kept at or near full throttle. As soon as the engine slows, it shuts off. There doesn't seem to be any engine miss and I was able to drive it home by making many restarts and hard accelerations. I did observe (on a long stretch of road) that the car would only go 90MPH.

Have some one tap it for you while you're under the hood to track it down and then disconnect at least one of the wires. You can also try looking at your fuse box or where ever your relays are and look for the horn or horn picture. Either of those should do the trick so whatever's easier.

P0306 PONTIAC - Cylinder 6 Misfire Detected https://www.autocodes.com/p0306_pontiac.html

P0141 PONTIAC - O2 Sensor Heater Circuit Malfunction Bank 1 Sensor 2
P0141 Pontiac O2 Sensor Heater Circuit Malfunction Bank 1 Sensor 2

check your fuel filters, fuel line, and fuel pump

When you say it shuts down do you mean "dies"? If so try checking your fuel pressure regulator.

After it dies is the security light flashing?

that would be your o2 sensor most likely. make sure its plugged in properly and that its not bad.

t.p.s. censor

Maybe weak fuel pump. It pumps when you turn the key on (fills fuel lines) but it dosn't pump enough to keep the car running. Could also be a partially cloged inline fuel filter.

Known GTP problem.

You most likely have a bad fuel pump resistor, which controls 2 speeds of the fuel pump.

To check to see if this is the problem, there is a trick you can do and its very easy to do. Go to the attached link, and bend the tab my finger is pointing at and then plug it back in. If your car starts and runs fine, well we just solved the problem.

Link ->> http://www.boredandstupid.com/relay.jpg

Make sure it always gets premium fuel...even with premium and especially in warmer weather the GTP will frequently perform the factory programmed KR (knock ******.) In WOT it is also more susceptible to running a lean condition with stock programming.
Things you can do to troubleshoot the problem and give more consistant performance with the GTP is run colder range copper core plugs and/or any brand of cold air intake, or even a stand alone 9" open element cone filter. Both are better than stock and provide more airflow even though the stock airbox was redesigned in '99. What else you can do is not limited to that but a start. Good luck.