Combine brown sugar and seasonings; rub over roast. Place roast, fat side up, on a rack in a roasting pan. Bake, uncovered, at 325° for 2 hours or until a thermometer reads 160°. , Remove roast from pan. Pour pan drippings into a large measuring cup; add water to measure 2 cups. Place flour in a small saucepan; stir in pan drippings until blended. Bring to a boil over medium heat. Cook and stir for 2 minutes or until thickened. Serve gravy with roast.