help! I'm having issues too. Replaced all heater hoses to bunk and cab. replaced heater control valve under heater core on cab and the control cable too. Been running with it now for three days and still no heat. I put new valves on all 4 lines, send and return and all are open no heat in front or back. Coolant level good. Is there something I'm missing? 2003 t-600.both front and back are same set up basically and I blew air through both and did a light pressure test on them both to insure no leaks. Took the lines off the front today and switched them still nothing so put them back to normal position. Even with ac and recirculate buttons off and heat control all the way to hot.... Nothing. Heater valve is moving good and correct. ??? I had water pump and thermostats replaced in July 2014 any direction will help thanks in advance. Mike