IT doesnt sound like its moving fluid very well in cold weather. I had one similar transmission that would get all crazy when I parked it nose up a severe driveway all day. When leaving, it flared and complained until the fluid got resettled.

A possible scenario for the better shifts after pulling over might be that the transmission has an opportunity to move fluid where it ought to be.

Like you I dont know squat about automatics, but I vote for a defective front pump or torque converter.