Mix Dr Pepper, Seasoning, oil and mustard in small bowl. Reserve 2 tablespoons marinade for brushing. Place chicken in large resealable plastic bag or glass dish. Add remaining marinade; turn to coat well.
Refrigerate 1 hour or longer for extra flavor. Remove chicken from marinade. Discard any remaining marinade.
Grill chicken over medium heat 7 to 8 minutes per side or until cooked through, brushing with reserved marinade halfway through cooking.