In 3 1/2 to 4-quart slow cooker, combine all ingredients except buns; mix well.
Cover; cook on low setting for 10 to 12 hours.
With slotted spoon, remove beef from sauce; place in large bowl. With 2 forks, pull beef apart to shred. Add 2 cups of the sauce from slow cooker; mix well. Spoon mixture into buns. If desired, serve with extra sauce.