MIX first 6 ingredients until blended. Place meat in slow cooker; top with sugar mixture. Cover with lid. Cook on LOW 7 to 9 hours (or on HIGH 5 to 7 hours).
TRANSFER meat to cutting board. Let stand 10 min. Meanwhile, use ladle to remove liquid from slow cooker; set aside.
PULL meat into shreds with 2 forks. Discard gristle. Return meat to slow cooker; stir in barbecue sauce. Gradually stir in reserved liquid if thinner consistency is desired. Increase heat to HIGH; cook, covered, 15 min. Serve in buns.