I've already asked about why my 2000 Pontiac firebird formula smokes dark grey but forgot to say that it over heats also

It might be helpful if we knew what engine you have. You said it has 171,000 miles. Does it still have the original water pump? Is the radiator plugged up? How is the cabin heat? Has the coolant ever been replaced? --- The radiator could be clogged. The water pump impeller may be eroded. There might be air in the cooling system. The thermostat might not be opening. --- Those are all common problems in older motors.

smoke can fool you, grey often is just moisture, gone when through warm up,blue is oil burning in cylinders,with combustion,black comes out as unburned fuel ,a very rich mix,as you say dark grey,fuel and water,ck. head gasket, or other reasons,like a gasket letting water in,fouling the reading of o2 commanding a rich mix,gasses restricting cirulation theirfore overheat ,open rad cap place hand on hole feel for pressure pumping from combustion,on a cold start, maby

How long does it take to overheat ? Have you had to add any fluids? Is the gauge telling you it's hot or is it actively blowing antifreeze after or before it over heats?

It's a Firebird Formula. That means it has the LS1 motor.