In a medium bowl, whisk together the brown sugar, lemon juice, white vinegar, cider vinegar, Worcestershire sauce, molasses and mustard. Season with granulated garlic, salt, pepper, red pepper flakes, white pepper and cayenne pepper, and mix well. Set aside.
Preheat an outdoor grill or smoker to 225 to 250 degrees F (110 to 120 degrees C).
Rub ribs liberally with barbeque seasoning, then place them in the smoker or grill, and cover. Cook for 4 hours, or until very tender. The meat will easily separate from the bone. Baste ribs with mustard sauce liberally during the final 30 minutes. Heat remaining sauce to a boil, and serve on the side.