Luke warm heat until set to 85+

[Dante04SRT]

Since the temps have started coming down, I've had to use the heat more in my '05. I was driving down the interstate tonight and the truck's digital HVAC was set to 80* and it still felt cool to me... it wasn't until I set the truck to 90* that it felt normal-ish again and was hot. It didn't seem to matter whether I was moving or stationary, the temp never felt right when it was set below 85*.

Before anyone claims head gaskets, let me give some more info:

- First, my degas has never puked.
- I have the degas bottle "full" at the lower mark and I haven't had to add any coolant.
- My ECT at cruising speed tonight was 180* (where its always been; even right after changing thermostats in May 2011 when I switched to ELC and did coolant flush)
- No loss in power
- Great mileage (19+ mpg @65mph)
- No smoke or other anomalies

After I got home tonight, I popped the hood, checked the level and unscrewed the degas cap to see if it seemed like there was an excess of pressure - There didn't appear to be... I have a pressure test kit for the cooling system but honestly don't see if being HGs this go around.

The only thing that has changed recently is I did replace my FICM last Saturday. Obviously, to change a FICM you have to really move the degas bottle out of the way quite a bit. Could that have disconnected something without causing a leak? How about the blend door? Is there a way to check it w/o tearing into the dash?

Any help would be great - We're supposed to be leaving for a cross country trip on Saturday!

[mhatlen]

I know that people having been posting problems with their duct not shutting correctly and air is not going across heater core. Honestly not sure where to start but my guess is a shutter is froze up on yaa.
Someone will chime in, Nice mirrors BTW.............

Is the vacuum hose connected to heater core valve,look closely for it in the open and shut position. Good Luck with it.........