Put roast in slow cooker crock. Stir cream of mushroom soup, beef gravy, brown sugar, dry onion soup mix, vinegar, soy sauce, Worcestershire sauce, salt, and pepper together in a bowl; pour over the roast. Cook on High for 6 to 7 hours or on Low for 12 to 14 hours. Remove roast to a platter. Ladle liquid from the slow cooker into a saucepan and bring to a boil. Sprinkle flour into the liquid and stir; cook until the liquid thickens into a gravy, about 5 minutes. Serve gravy with the roast.