09 Ram 1500 driver side window will roll up but only roll down intermittently

If, when you engage the switch to roll the window down, the window does not move but you still hear the motor operating - then clearly, the motor is getting power as needed from engaging the switch. It would next be necessary to remove the driver's door panel and inspect internally for the source of the problem, such as the window regulator mechanism binding causing the motor to strain going down.