I have a 97 Ram w/ 5.9. Has a new water pump, thermostat and flushed the heater core. Have heat for a little while standing still then start to drive- heat is gone. Checked the radiator hoses - before driving warm and hard, after drive cold and soft- both hoses. Acts like no coolant movement. Where do I go next?

 

It's possible that one of your hosesis weak and is colapsing while you drive, cutting off the water flow.