Place potatoes in 5 qt. slow cooker, trim fat from roast, cut in half. In large skillet, brown roast in oil on all sides, transfer to slow cooker. Reserve 1 T. drippings, saute onion in reserved drippings until tender. Stir in tomato sauce, brown sugar, worcestershire sauce, vinegar and salt. Pour over the roast. Cover and cook on high for 4 to 6 hours or until meat is tender. before serving, pour sauce into a skillet. Cook and stir over med. high heat until reduced and thickened, serve with potatoes and meat.