2004 Sebring low heat from dash

[rexf]

2004 Sebring 2.7 L v6 133,300 miles.
Replaced - Water pump, timing chain, thermostat, blower resistor. All of these were bad and have had no effect on the low heat.
Issue - low heat coming from dash heater (approximately 100 degree discharge on a 40 degree day). If you turn off fan for a minute then back on there is more heat but only for a few seconds. Heat builds up in box then discharges. Cool again after.
Checked - Flow through heater core appears to be good and clear (water hose test). core is not leaking.
Blend door actuator appears to be working correctly. Will cycle between heat and cool. Visual inspection of actuator operation looks good.
Mode door actuator appears to be working correctly. Cycles between upper and lower registers and defrost.
Hoses do not appear to be collapsing. Do not see any restrictions in hoses.
Thermostat appears to open at mid gage level, about the same time as the radiator fans. Water temp drops a bit and then it cycles closed.
Any clues what I am overlooking?