well you could look on the bright side it closes most of the way which means.
1. It most likely is a spot on the armature that is getting really glazed,, and eventually it will decide not to come down out of "park".
2. these windows usually have a type of spring to assist the motor , in the regulator , springs wear out. It would not have the push at the top ( I am not 100% sure it is this design though.
3. There is a voltage drop across the switch when it is operating ( bad switch ), that is not allowing the motor to get the full wattage , voltage drops elsewhere in the wiring will also have the same effect.
4. the window is not adjusted correctly( there are two guides front and back ) and it is binding at the top.
5 a combination of the above factors.
Measuring the voltage at the door window motor is the simplest way to differentiate what is what.
Voltage across the motor should not be significantly less than battery voltage.
If it (voltage) increases at the top when it stalls it is a motor opening up, and drawing less current.
expected reading is about 10 to 12 vdc , which is dependent on the factors of track adjustment , lubrication etc.
Inspect everything , especially for loose attachments at the window itself.
Good luck .