Season meat with salt and pepper and place in a 9 by 13-inch pan, and cover with onion. Combine ketchup, chili sauce, sugar, garlic and beer and pour over meat. Cover with foil and bake at 300 degrees for 4 hours. Remove foil and bake uncovered for 35 to 40 minutes. Remove meat from pan. To make gravy, with an immersion blender or a blender blend all liquid from the pan. Cook and stir until thick. Cool meat and slice cross-grain. Lay in baking dish and reheat. Serve with gravy.