Dodge Ram Heater Not Working Properly?

I drive a '02 Ram 1500. I have no idea whats going on with my heat. The passenger side blows hot air, but it cools down. And the drive said blows cool air. I've replaced the heater core, and the thermostat twice. I also replaced the radiator. I've gotten all the air out of the lines. I'm not sure if it's just a vent in the hvac unit. The top of the dash is missing and when I drive with my window open I can hear one of the vent doors open and close really loudly.