Here's the summary:
-temp gauge normally sits at about 50% (i.e., just below dot in center of range), but suddenly won't go above about 10% (or ~1/8th from the bottom)


Background:
- I lost all heat several months ago, so pulled the old thermostat and it was cracked. I read up on how to replace it here, then bought a high quality thermostat (92 C) and installed it. (I can't be completely certain that I put it in facing the correct way, as I was so interested in how it cracked that I had it in my hand before realizing that I hadn't noted which way I pulled it out).
- after installing the new one, the temp immediately read a little lower than it had prior to the the replacement.
- it maintained an even temperature at about 40-45% of max for several months throughout a cold Colorado winter.
- after sitting for a week, the guage stayed at about 10% for 100+ miles, BUT there is ample heat coming from the heating vents.

Can the guage stick, or could something be blocking the thermostat?

Thanks,
Mike