A door window may move slowly or stop in mid travel due to a failing power window motor. The affected window may start working again after the motor cools off. Replacing the faulty window motor will commonly correct this concern.Google+
Car Problem Reports
GMC Safari Power Window Motors May Fail From Overheating
GMC Safari Problem
Average Mileage: 110,833 mi (65,000 mi - 180,000 mi)
both power windows exhibit the problem described with overheating. Windows travel down ok initially, but I have to wait while moving it up for the motor to cool. Eventually both will go up
Visitor, 2001 GMC Safari, 65,000 mi
Power window motor stopped working and was replaced by my mechanic who said pieces of the gear had broken off. Less than a month later the window began "shuddering" as it went up and down. It was trying to go up 1/2" farther than the frame and I was afraid it would shatter. I saw that it was going up 1/2" too much then dropping back down to where it should have stopped. I haven't had the money to get it fixed again.
Visitor, 1991 GMC Safari, 180,000 mi
Power Window switch failure. Button Detached from switches before complete failure. Probably switch replacement needed but could also be motors. Left as is.