Slow Cooker Root Beer Barbecue Beef Sandwiches

(From BettyCrocker.com)

1 boneless beef rump roast (4 lb)
2 cups barbecue sauce
1 cup root beer
Dash salt and pepper, if desired
16 sandwich buns, split

1. In 3 1/2- to 4-quart slow cooker, place beef. In 4-cup measuring cup or bowl, mix 1 1/2 cups of the barbecue sauce and the root beer; pour over beef.
2. Cover; cook on Low heat setting 10 to 12 hours.
3. About 20 minutes before serving, remove beef from slow cooker; place on large plate. Pour juices from slow cooker into 12-inch skillet. Cook over medium-high heat about 15 minutes, stirring occasionally, until juices are thickened and reduced to about 3 cups. Meanwhile, shred beef with 2 forks; return to slow cooker.
4. Stir remaining 1/2 cup barbecue sauce into reduced juices in skillet; pour over shredded beef in slow cooker. Stir in salt and pepper to taste. Spoon about 1/2 cup beef mixture into each bun.