Heat?

[6768chevylover]

Alright.. This seems to be an on going thing for me due to the winter weather.. I have replaced the heater core about 3 months ago, the thermostat around the same time and just replaced the radiator on presidents day.. The heat is nuke warm and when I drive it gets a little better and cools down when I stop.. There is a possibility that air is in the heater core lines I understand that but, then why would the temp go up and down while I'm driving? Could this be a water pump issue all this time? how do you know it its bad? I don't hear any whining noises or such.. Thanks, Mike