Arrange chicken pieces in slow cooker. Combine lemonade concentrate, brown sugar, ketchup and vinegar mix well. Pour lemonade mixture over chicken. Cover and cook on HIGH for 3-4 hours. or Low 6-8 hours. Remove chicken from crockpot and cover to keep hot. Transfer liquid to saucepan over medium-low heat. Skim fat; combine cornstarch and cold water and add slowly to liquid, while stirring. When thickened, serve with chicken along with hot cooked rice.