Power Window Problems

I am experiencing a problem with the drivers side front power window on my 93 G20. For awhile it seemed to struggle on the way up and finally it got stuck in the up position (better than down). I have read a few of the threads posted here and thought I had it figured out. I pulled the door panel and tested the motor which worked as expected. I then thought it was the amplifier (white box), but I checked and am getting 12 volts through the amplifier to the motor. I hooked everything back up and it started working again. It is still very sluggish, but so are all the other windows. I had already purchased a new amplifier so I hooked it up and everything worked, but was still sluggish. I tried greasing the cables and track, but that really didn't help. One thing that I noticed was that the motor got extremely hot, hotter than I would expect. Is this normal??? Anyone have any idea what it is? Should I go ahead and change the amplifier or will I be wasting my money? As a side note I learned a valuable lesson and will always go to the Nissan Dealer first for parts. The part was 35% cheaper at Nissan rather than Infiniti.

I AM HAVING THE SAME PROBLEN. mY WINDOW WORKS ONLY WHEN I HOOK THE MOTOR STRAIGHT TO THE BATTERY. I THOUGHT IT MIGHT BE THE SWITCH OR THE WHITE BOX. I TESTED THEM AND THEY SEEMED TO CHECK OUT. I CANT FIND OUT WHAT IT IS.. IF YOU CAN HELP IN ANY WAY SHAPE OR FORM, IT WOULD BE GREATLY APPRECIATED. tHANKS!