2000 chevy malibu overheating, and blows cold air when the heater is on?

[[]DLAYETTE]

I have a 200 chevy malibu that started overheating. Replaced the thermostat, radiator, water pump, heating sensor, and one of the hoses that connects to the engine. Did a radiator flush also. During the radiator flush turned the heater on high, and it was blowing cold air. Antifreeze/coolant will come out of the overflow hose when the car is running sometimes and when the car is shut off. Could it be the heating core?