Trim excess fat from the meat. Place roast in slow cooker, cutting in half if needed to fit. Add onion.

In a medium bowl, combine soup, vinegar, bouillon, sage and pepper. Pour into slow cooker over meat and onions.

Cover and cook on high 4 1/2-5 hours or on low for 9-10 hours until meat is very tender.

In a small bowl, stir together water and flour until smooth. Stir into boiling liquid around the roast. Cover, and cook on high for 15-20 minutes or until thickened.

Serve meat and gravy alongside your favorite potatoes or grain (I like mine with rice).