I don't know what's wrong with yours but on my '99 the driver's side went out.
I paid $110 for the motor, tracks, cable etc. from these guys. It's all one big assembly. It fit. It works. I don't use it a lot.
They have Chinese versions for less.
http://www.1aauto.com/1A/WindowRegul...olet/Silverado
I think the job took an hour or so.
I recommend taping the glass to the top of the door before removing the mechanism.
I used directions from Crutchfield to remove the door panel. These are different but pretty good.
http://www.a1electric.com/silverado2.htm