Place brisket fat side down in a large slow cooker. Spread garlic evenly over brisket; sprinkle with pepper. Arrange onions over brisket; set aside. In a large bowl, combine sauces, ale or broth and brown sugar; pour mixture over brisket and onions. cover and cook on low setting for 8 - 10 hours. Transfer brisket to a cutting board; tent with with aluminum foil and let stand for 10 minutes. Stir liquid in slow cooker; spoon off fat and discard. Arrange brisket on platter, spoon liquid over brisket before serving.