Losing Heat while idleing on 2002 Dodge Ram 1500

I lost heat in my truck. I replaced radiator,thermostat,radiator cap,and water pump. Heater core is good. I have heat when I accelerate or rev engine. Once I come to a stop or truck is in idle i lose heat. Anyone have any ideas?

Asked by for the 2002 Dodge Ram 1500
It sounds like your heater controls are not working, i.e. the heater control valve which may be vacuum controlled, which would explain the erratic behavior with the engine speeds etc. Or, it could be a heater door inside your heater plenum that is vacuum controlled that is not working OK etc. go here for the info on your Truck:

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