Kragens sells lifetime warrantied rebuilts for $60 per side, they are special order though.. only took 1 or 2 days to get it though.. my drivers side was reallll slow too ('77 GMC) and MAN is the new one fast.. REAL fast, I like it though.. only thing is its kind of noisey but it works good..
you might want to try using lithium grease first on the rollers and stuff, or at least WD40...with manual crank windows, it ALWAYS helps, not so much so with power windows though, from what Ive noticed.. you dont have to remove the glass to change the motor.. what I do is remove the door panel, then put the window all the way up and duct tape it from one side, up around the door and down the other side, that'll hold it.. might have to remove the 4 bolts holding the motor&scissor assembly first.. once you do it, you'll be able to do it soooo much faster & easier.. but just remember, it will all come out through the square hole in the door, the one a little low and to the right of the lock. prepare to cuss a lot & cut up your hands a little, fooling with the assembly through that hole cut in the sheetmetal.. when you unbolt it, have the windows roller upper switch handy, and the power still connected because you may have to "raise" or "lower" the motor a little to make it fit through... just be patient and it will all come together nicely.. good luck..
mike