heater is luke war, have to leave on high all the time, heater core hoses are equally luke warm, there is a inline vqlve in 1 heater dore hose at firewall, no vacuum port on it or linkage just a cap says keep tight, dunno if thats a control valve or flow valve? temp guage reads normal, has the digital heater/ac control, does work as air gets cold when drop the temp, so blend door seems fine, im banking on this valve inline of the heatercore hose, had several 97 to 03 trucks never seen this b4, must be due to the digital heater control in dash, thinking of removing this valve?