Not sure if the problems are related but they started about the same time. When I'm at a light or at low speeds temp starts rise to around 200 even with both fans on which used to keep the car at a constant 170. As I pick up speed tempature continues to rise all the way to the red in the span of less than a minute. It'll hold there for a few seconds then come down to normal temp just as fast. My heater, cranked all the way blows nothing but cold air even with the defrost on.

I've flushed the system, changed the thermostat and the CTS with no luck. Please help!

 

sounds like you classic air damn problem. look under the front of your car and look for a piece of plastic hanging down that is cruchial (i suck at spelling) to keeping your car cool at highway speeds.. i had the same problem for about 3 months and had to put my car away for a long time till i came across this sight. now car is the beast running ever!

 

as far as the heater, the heater duct might not be opening..

 

It could be the head gasket. My friends mustang did the same thing and his head gasket was blown. He replaced a water pump all radiator hoses and a thermostat and it ended up being the head gasket

 

Your water pump might be shot. I just had the same problem. Do you notice any leaking of coolant leaking from the front of your engine or loss of coolant in your reservoir? These are possible signs of a bad pump. I replaced mine and everything was good again.