2001 Pontiac Grand Prix

A severe enough vacuum leak will cause your engine to shut off, but it won't have anything to do with an overheating situation.

If you didn't torque your head gaskets correctly, you'll have a leak that will cause exhaust gases to enter your coolant, and that will cause overheating.

Also, check your oil for coolant. Next, bleed you coolant of all air. Then have someone rev the engine to at least 1,500 rpms while you remove the radiator cap (or surge tank cap). At the very same time as the motor reving up, look inside the coolant. If you see large air bubbles, then that is exhaust gas.

If you don't see bubbles, make sure there's no coolant exiting the tail pipes.

If you have no problems with the head gaskets, and you've bled the system of air, then you'll need to check for an obstruction in the system and/or a failing water pump or thermostat.

To check the thermostat, feel the upper and lower radiator hose after the engine has warmed up a bit. To check the water pump, squeeze the upper radiator hose while someone revs the engine up. After the thermostat opens, you should feel the pressure as the water pump turns faster.