While driving at 40 or 50 my heater works fine but when I go faster my temperature gauge drops and the heater will only put out luke warm air.
No one I've talked to has ever heard of this problem before. I had the thermostat changed and that did not help any.
Please......somebody help.

 

when you go faster you have more ram air across radiator
therefor making the coolant cooler
therefore making your heat cooler
check to make sure you have a correct mix of antifreeze and water
also check to make sure your fan isnt running all the time
good luck

you could put a pizza box on front of radiator
less ram air less cooling it would get hot then