1. Heat oil in Dutch oven over medium-high heat until hot. Add beef roast; cook until browned on all sides, about 10 minutes. Place beef in 3 ½ or 4-quart slow cooker.
2. Add 2 tablespoons root beer to Dutch oven; cook and stir, scraping up brown bits. Pour mixture into 4-cup measuring cup or bowl. Add 1 ½ cups of the barbeque sauce and 1 cup of root beer; mix well and pour over beef.
3. Cover; cook on low setting for 10 to 12 hours.
4. About 20 minutes before serving, remove beef from slow cooker; place on large plate. Pour juices from slow cooker into 12" skillet. Cook over medium-high heat for about 15 minutes or until juices are thickened and reduced to about 3 cups, stirring occasionally. Meanwhile, shred beef with two forks and return to slow cooker.
5. Stir remaining ½ cup barbeque sauce into reduced juices in skillet. Pour sauce over beef in slow cooker. Add salt and pepper to taste and mix well. Spoon about ½ cup of beef mixture into each bun.
Makes 16 sandwiches.