heater in side works very good when you are going down the road but when stopped. on 1996 Dodge Ram 2500

when you stop the temp goes up and up then you start going again then the temp goes down and down don't know why. the A/C works very good its not that can some one help me.

Asked by for the 1996 Dodge Ram 2500
you might wanna check your coolant level, make sure the fans are working. the reason the car cools when your driving cause air circulating in the engine compartment helping cool the engine. When you stop the fans are supposed help circulate air cause you are not moving.
thank you very much I will try it and check out the coolant level.
Thank you