It is an '06 Impala with less than 70K. It prevents me from warming it before l get in and drive. It gets REALLY HOT after about 5-10 mins of driving.

Sounds like a vacuum leak to the vent doors.

the heat probably does that because........
the heat from the engine goes through the heating ducts. when you accelerate, you kind of rev the engine, which makes the engine get a little hot. that heat goes from the engine, through the vents into the car.

the heat blows out really hot air after ten minutes of driving because the engine has warmed up a lot around that time. so the hot engine air will go through the vents and into the car.

it sounds like u might be a little low on coolant,or there might be an air bubble in the coolant system.check the fluid,if it is good maybe u should go to a mechanic.

Do you need a new thermostat?

check and see if the thermostat is in there if it is maybe it is stuck open had this problem on a chevy lumina