My guess would be some broken wires in the tunnel between the door and the body, it does happen, you will have to remove the door panel and kick panel to gain access and then pull in new wires through the tunnel one at a time and then solder and heat shrink wrap the connections. Do just try splicing the wires in the tunnel, it puts more stress on the wires and they will break again in a short period of time.
2006 Buick Lucerne driver side window goes down easy, only powers up halfway and stops, need to keep hitting the up button and rocking the window to get it all the way up.
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