I have replaced every part in my 94 f150 coolant system,(some more than once!) Three T stats later and 3 "burpings" later my heat puts out lukewarm air when driving and the temp goes from O to almost L but doesn't over heat. When idling temp remains between O&R and I get good heat like it should work when driving. I have replaced wpump,hoses,heater core,fan clutch and radiator. Any ideas would be apriciated! Thanks in advance.