Combine first 5 ingredients; rub over roast. Cover; refrigerate overnight., Place carrots, potatoes and onions in a 6-qt. slow cooker; add broth. Place roast in slow cooker. Cook, covered, on low until meat and vegetables are tender, 8-10 hours., Transfer roast and vegetables to a serving platter; tent with foil. Pour cooking juices into a small saucepan. Mix flour and water until smooth; stir into pan. Bring to a boil; cook and stir until thickened, about 2 minutes. If desired, add browning sauce. Serve roast with gravy and vegetables.