[ImperialCrown]

Is there about 12 volts at the motor terminals going up or down?
A high resistance in one side of the switch contacts will drop the voltage too low to lift the glass.
Maybe the 'up' contacts are burnt?
The switches do come apart and the contact points can be filed and burnished to improve contact. A drop of Deoxit on the contacts may preserve them.

 

[TM1963]

I had a problem similar to, but not exactly like yours. My window would go up, then about 3" from the top - would slow down and pop out of the tracks/guides - the top back would be sticking outside the car. In my case - it was a friction issue - put some WD-40 (didn't have any silicone/teflon which should be better) - and it started working better than ever. (I had replaced a regulator just 2 months prior - and it failed, replacement for that - popped out - I thought was defective, then the NEXT replacement did the same thing).