Are you running gear oil or UDT/SUDT in the gearbox? I have run my tractor in twenty degree weather only a few times. The 3pt has been real sluggish but gets much better once I start moving the tractor around. I run 80w gear oil. One thing I do is engage the pto and let it run (no pto implement on) while the tractor warms up to help 'stir' the tranny fluid.
I wouldn't think the 3pt speed bolt/knob comes into play while raising the 3pt but maybe and the oil is thick enough for it to restrict more than usual.
You may have water in the system that is causing an ice blockage, likely in the two hyd lines that run up the left side to the pump on the side of the engine.
Charles