A sliding window panel assembly for a motor vehicle. The assembly includes a stationary window panel having an opening formed therein, at least one guide rail coupled to the stationary window panel below the opening and above a bottom edge of the stationary window panel, a shoe slidably received within the guide rail and configured to slidably move within the guide rail, a movable window panel mounted onto the shoe such that the movable window panel slidably moves with the shoe. The movable window panel can slidably move with respect to the stationary panel along a movable panel path. The lead screw drive unit engages the shoe and is adapted to move the shoe and the movable panel along the movable panel path within the guide rail.