Blend door repair or not...96 Ranger

[5greenmonkies]

I have a 96 Ranger, 4 cyl, 2WD with ~197K miles, and it runs like a champ. A new irritant has reared its head, which I'm thinking requires the blend door fix but I'm not sure.

My heater will not maintain its temperature as I increase the blower speed. In other words, the heat temp is fine on the lowest blower setting but cools down quickly after I turn up the blower speed. Does this sound like a blend door fix? I've replaced the thermostat (engine temp was showing low, but that didn't fix the temp gauge problem).

I still get 20mpg and everything else is running fine. Thoughts?