Window will only role up and down part way untill truck restarted

This truck is a 1985 GMC G1500. The trucks window will role down half way and then role back up almost to the top, it makes it some times, but after this I can't move the window anymore, not untill I turn the truck on and off again, as a matter of fact, I can role it down half way turn it off turn it back on and role if all the way down, but never all at once. Also once I've rolled the window down as far as it's decided it's willing to I can role it up part way and I'm unable to return to the point at which it was just resting, it's like it ran out of downward motion in the initial role down then no mater where the windows positioned it won't role down again untill the powers turned off and back on again, and I don't think it's just a week motor because even if I press the switch down and try and help the window move it won't go anywhere it feels locked in place.