Might be a bad motor, or dirty connections. Run 12v directly to the motor and verify operation. You can easily check grounds and voltages with a basic multimeter.
Since you have a working drivers window, that rules out the relay, and fuse.
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1976 LeMans B09 Freeway Enforcer, 455/M40 Smokey
1977 Trans Am, 400/M21 Black/Gold Bandit. 44K actual miles
2017 Sierra SLT 1500 Z71 4X4 
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