I had to change the switch and the rollers on the window regulator to get it perfect. This is how I found out:
I baught my Corvette from my cusins friend. My cusin used to have it befor her again.
Anyway, when my cusin had it, she suddenly couldn't get the window up. They tore out the motor and got the window up and fastened it there with a plyer and never replaced the motor.
When I baught it years after that, I baught a new motor and put it. It still wouldn't go up, but it did go down. I also messured the power and ot 12 v both up and down. As fast as I put the plug in the motor and got some load on it, it would go down but not go up. The power dissapeard.
I changed the switch and it started working right away. But it went up really slow. So I tore the window regulator and the chanels out and replaced the rollers and put new lubricant on. It works as a dream. The old rollers would hardly turn because of old and hard lubricant. I will be doing that on the driversside too.
Hope this helps if anyone has the same symptoms as mine....