Pat chicken dry. Combine rub ingredients. Rub over chicken pieces; refrigerate, covered, in a shallow dish 2 hours., Meanwhile, in a small saucepan over medium heat, combine sauce ingredients, adding cayenne if desired. Bring to a boil, stirring constantly; reduce heat and simmer, uncovered, to allow flavors to blend, 8-10 minutes., On an oiled grill rack, grill chicken, covered, over indirect medium heat, turning frequently, until a thermometer reads 165°, 35-45 minutes., Reduce heat to medium-low. Brush chicken with sauce, reserving 1/2 cup. Cook, covered, until chicken pieces register 170°-175°, 4-6 minutes. Serve with reserved sauce.