In a small bowl mix together sugar, paprika, mustard, cumin, garlic powder, onion powder, cayenne, 1 teaspoon salt, and 1 teaspoon pepper. Set aside.
Trim and pat chicken drumsticks dry.
Rub seasoning mix all over the chicken until it is well coated.
Put chicken in a 5 quart slow cooker, and pour ½ a cup of barbecue sauce over the top.
Cover and cook until chicken is tender 4 to 6 hours on low.
Position your oven rack 10 inches from the broiler.
Preheat oven to broil on high. Line a baking sheet with foil, and place a wire rack over the top. Spray rack with cooking spray.
Take chicken out of slow cooker, and place on the rack over the lined cooking sheet. Discard and cooking liquid in the bottom of the slow cooker.
Brush chicken with ½ cup of barbecue sauce, and broil until crisp (10-15 minutes)
Flip the chicken over and brush with the remaining sauce. Broil for another 5-10 minutes.