Car doe4s the exact opposite of what it should do? when I slow down or stop the heat gets colder, when I speed up or am at hiway speed the heat is fine? any ideas or sugestions? car doesnt run hot coolant level is fine? im stumped

Pull off both heater hoses at the pump and flush both ways with a garden water hose.

ill do that tonight and report back I might as well replace the hoses while im there

is you alt charging??

do you have low/lower vacuum at idle? some of the heater controls and actuators in the heater box are vacuum operated. a dry rotted vacuum line under the dash could be causing the issue...

I don't know about the later Dippys, but Dad had a 1980 that developed a strange problem, heater temp would vary as the car was driven. Eventually we noticed that it would happen consistently on turns, turn one way and you'd get heat, turn another way and you'd lose it.

After noticing that, we listened and could hear the heater blend door, which blends the amount of air going past the heater core, closing sometimes when the heat output would change.

End result:
The dealer diagnosed a 'servo'as the problem, which caused me to investigate the vacuum pods (but no avail). Problem persisted, so I got more info from the dealer.

The servo is mounted on top of the heater box and it contains a small electric motor and some electronics to control the blend air door. I presume it is some type of crude stepper-motor setup. The factory had rebuilt ones available, and it seemed like we had to replace them every few years after the original one died.

The top metal of the dash was the easiest way (perhaps the only way?) to access it. Servo was a black plastic box about the size of 2 packs of cigs.

Again, that was a 1980, later years might be different.