Satisfactory operation when warm proves the motor and wiring are okay. A common cause of sluggish response, worse when cold, is road dirt, tar, or bug juice in the rubber window channels. Spray them liberally with Silicone Spray Lube. It goes on like water, then evaporates and leaves a film of "slippery" behind. I use the stuff from the Chrysler dealer but it is available from any auto parts store or hardware store. It works real nicely for dragging seat belts that don't like to retract properly. I spray my belt webbing about once a year on my '88 Grand Caravan.