Well if its hot their or in he hot sun. Wait till it cools down. Get where its cool and think about what all it could be. Working in the heat and sun can makes things alot more miserable and harder. Step back and take a good look at the seams and the window are. .Then think about the motor. Old dried up grease can be your problem in the motor. Then it could be inside the tail gate.A bad wire. You,ll find it and I have confidence in you--we all do..Just take your time and you,ll see the problem--remeber 3 areas-alignment of window---motor and tailgate area parts.