Have a 78  passenger side window goes up and down really sluggish drivers side works well with no problem. any ideas on  why it has to work so hard. or where to look. to correct the problem. could it be maybe motor is tired or  ?  Any help would be appreciated.
 
         &nbs p;       Mike

Could be the motor, or could be that the regulator needs a little lubrication. Pull the door panel off, and see if the regulator looks really dry. There are several points where the mechanism pivots(sissors), and sometimes a little WD-40(or similar product) will help. Make sure the tracks(where the rollers "roll") have a little "white" grease on them, and that what is there is not hard as a brick! If lubricating the mechanism doesn't help, it may be time for a new motor .

Does it matter if the door is open or closed? Sometimes, the weatherstrip causes the glass to "drag" as you roll the window up. If it works better with the door open, use a little silicon grease,(made for rubber weatherstrip), and see if it helps the glass go up better.

The motors are usually good or bad. It is possible but not probable that there might be a bad ground. Most times it is binding in the regulator or weatherstipping interfering with the glass. Do you here any grinding or knocking when the window is traveling up and down? If so, it is probably in the regulator. Someone here will be able to help you. I am amazed at the knowledge found here.
Good Luck!
Scott

there is no grinding or weird noises just goes up and down real slow, sounds like a plan to do this weekend take the panel off and lube up all the rollers and pivot points and go from there. does not matter also if door is open or closed still the same. thanks for for the info it is greatly appreciated. 

replaced mine on passenger side.. what a difference.. $50  Advance. Had to modify the wiring as I  didn't like the way the wires connected with the universal aftermarket..(seemed too loose). Will be doing driver side soon...

Make sure you have a good connection at the switch too. And make sure the wires are secured and out of the way of the emergency brake... I had the wire get caught by the emergency brake once, and it cut it in half...