Place roast in a 5-qt. slow cooker. In a small bowl, combine the broth, apple juice and mustard; pour over roast. Cover and cook on low for 4-5 hours or until tender. Remove roast and keep warm.
For gravy, strain cooking juices and skim fat. Pour juices into a small saucepan. Combine cornstarch and water until smooth; gradually stir into juices. Bring to a boil; cook and stir for 2 minutes or until thickened. Serve with pork. If desired, top with coarsely ground pepper.