My 2003 ram 1500 with 4.7 V8, no heat in cab after I start driving, I have replaced, water pump, thermostat, antifreeze. More info, when I drive with cold engine, as temp gauge starts to rise I get heat. As temp gauge reaches 12 O-clock and past I have not heat inside cab. Top radiator hose is hot, bottom is cold with engine at normal tem/gauge at 12 o-clock. Please email me direct at [email protected]

Try having a flush and fill of the radiaotr maybe your heater core is blocked