Originally Posted by kenified06
Yeah it actually seems to overheat even faster when at idle or when I'm off the gas
That usually is the fan cooling resistor. Your fans have 2 speeds. If the low speed is not working, the engine will overheat at idle. It will not overheat with the AC on because the fans run at high speed with the AC on.
You can check the temperature at which the fans come on by using the electronic odometer trick to monitor temps. Key off, press and hold the odometer reset button. Turn key on, hold odo reset button until the odometer reads [test]. Now you're in test mode, and you will remain in test mode until you turn the key off, and each time you press and release the odo reset button it will scroll through one of 30 test functions. The one you're looking for looks like this [30 C] or whatever your ambient temp is on a cold engine in C. Now this might sound goofy, but the fans come on at very high temperatures. Low speed is around 115C, and high speed is 118C. This engine is designed to run as close to overheating as possible.
Usually the low speed causes the sort of overheating you're experiencing, but since the high speed comes on- people think the fans are working correctly.
As far as the heater core goes, you can check it by removing it's hoses from the engine, and then flushing it out. I doubt that the heater core is the problem in this case, and wouldn't change one until it leaks inside the car.