Place Chicken In A 5-Qt. Slow Cooker. Combine The Lemonade, Ketchup, Brown Sugar And Vinegar; Pour Over Chicken. Cover And Cook On Low For 2-1/2 Hours Or Until Chicken Juices Run Clear. Remove Chicken And Keep Warm. For Gravy, Combine Cornstarch And Water Until Smooth; Stir Into Cooking Juices. Cover And Cook On High For 30 Minutes Or Until Thickened. Return Chicken To The Slow Cooker; Heat Through.