Sounds like you need to rebuild the motor (gear assembly and check the sliders that put tension on the glass.
First remove the door panel (of Course)
remove the power window motor. Remove the cover from the gear asssembly. You should see three oval shaped bushings in the gearset. If you don't and just see a bunch of garbage, then you need to replace the gear assembly or the bushings. I cleaned everything real well and found that the gears in mine were pretty messed up so I changed the entire gearset. You can get all of the parts from 50 Resto fairly cheap. You can even replace the motor bushings if you want to go that far into the motor. When you put the gear assembly back together, make sure to pack the gear housing with a heavy grease. I used a yellow grease I think (did this a long time ago).
I read an article on replacing the motor bushings, but the article said that most of the times you can get away with just cleaning the motor assembly real well. The article said that the position of the motors in the door let all of the dirt and sediment from the motor fall into the commutator/brush assembly and jam them up.
Next look ino the door and you should see two -three little tabs with felt on them. They are prbably worn to sh*&. Take the off and replace the felt, using a spray adhesive or try and get new ones.
After that since you will have the door apart already, get two window guide bushings from 50Resto and replace the guide bushings on the center rod that the window rides on. This will keep your window going up and down in a straight line, instead of tipping forward and backward.