In a large heavy skillet, brown roast on all sides.  Transfer to a slow cooker.  In a bowl, combine juice, tomato sauce, onion, vinegar, salt, cinnamon, and ginger.  Pour over roast.  Cover and cook for 10 hours on low or 5 hours on high.  With about 2 hours left on timer, add carrots and potatoes.  When meat is fully cooked, drain juice into large skillet.  Bring to a boil.  Meanwhile, in a small bowl, combine arrowroot powder and water until smooth.  Pour, while stirring, into cooking juices and heat until thickened.  Remove from heat.  Slice roast and pour gravy over top.