During a sledding trip to local mountains with four adults and three kids aboard, we did a little light off-roading in the Lincoln Navigator. Push-button four-wheel drive, big tires, generous ground clearance, and the thrill city folk get when ramming around the high desert in a gigantic luxury SUV sure provided passengers who repeatedly tested the automatic locking retractors of the seatbelts with a good time. From behind the wheel, however, the Lincoln is a dud to drive.