[mrein3]

Have you bled the system recently? Old, wet, contaminated fluid could be freezing in there - being that you are in Utah that is a possibility.

I would get all new fluid moving around the system and see if that fixes the problem. Use a turkey baster or similar and empty your master down to just above the ports that feed the brake lines. Fill it back up with new fluid. Then go from wheel to wheel until you get clear, new brake fluid out at the bleeder. Of course don't let the master go below the output ports or else you'll need to bleed the master.