1999 Pontiac Grand Am overheating

Hi, my name is juan and I have a tricky problem. It had to do with my temperature getting too hot. First of all let me say what i've had done to my car.I've done a pressure test, I had a new radiator installed, intake manifold gaskets, a waterpump, thermostat, a radiator flush, a new surge tank, new hoses but my car still gets hot. This is what happens and what I found out. When I start my car after its been sitting for a couple of hours I let it heat up till it gets to about 200, but after I take off the temperature rises to 280 and the red light comes on so I have to pull over and let it sit while I turn the heater on. So now what i've been doing is when I let the car heat up I turn the hot air on, but the air doesnt come out hot. The temperature keeps rising untill the heater blows out hot air, but when it does blow out hot air the temperature drops back slightly 200 and the car doesnt overheat and runs fine as long as the heater is on, what can this be