working.
Rolled the window down and it won't come back up. All other windows are working just fine. It makes a clicking sound when you push the button down for the window to roll down, and no noise when you push it to roll up.
thanks for any guidance.

 

Here is the logic of what you describe;
1. The motor runs.
2. Power is present.
3. Ground is present.
4. To run Up, the voltage and Ground applied has to be reversed at the Switch. DC Motors run both ways when reverse power is applied.
Since they are present for the Dn function and missing for the Up function, suspect the Switch contacts to be open preventing reversal of power to the motor.
Up function takes a little more power to move the weight upward and sparks the switch a bit more over time.
The GEM is involved in all functions but doubt it is the cause of one way operation because it's under your manual door switch control..
Otherwise the motor drive may be faulty from rust.
They have rubber boots that go bad after so many years and let water in and into the motor. This especially bad in winter when the water freezes in the motor and won't move until the cab gets warm. The window seals don't block all water from getting in.
Good luck.