Cut roast into quarters. Mix brown sugar, salt, paprika and pepper; rub over meat. Place meat and onions in a 5-qt. slow cooker., In a small bowl, whisk vinegar, Worcestershire sauce, sugar and seasonings; pour over roast. Cook, covered, on low 6-8 hours or until meat is tender., Remove roast; cool slightly. Reserve 1-1/2 cups cooking juices; discard remaining juices. Skim fat from reserved juices. Shred pork with two forks. Return pork and reserved juices to slow cooker; heat through. Serve on buns with coleslaw.