Cranberry-Barbecue Beef Sandwiches

1 c beef broth
1/4c instant minced onion
2 tbsp ground black pepper
4 lb boneless chuck roast, trimmed
1 c sweet hickory smoke barbecue sauce
1/4c brown sugar
1 c whole-berry cranberry sauce
16 (1 1/2-oz) hamburger buns

Combine first 3 ingredients in a Dutch oven. Add beef, and bring to a boil. Cover, reduce heat, and simmer 3 hours or until very tender, turning beef occasionally. Remove beef from pan. Reserve 2 cups cooking liquid, discard, or retain remaining broth for future use. Shred beef with 2 forks, then return the shredded beef to pan. Add reserved cooking liquid, barbecue sauce, brown sugar, and cranberry sauce, and stir well. Cook over a medium-low heat 10 minutes or until thoroughly heated. Serve beef mixture on buns.