In a large bowl, combine the ham, pork OR sausage, and the ground beef. Stir in the milk, eggs and graham cracker crumbs and mix well. Form into large balls about 2 inches in diameter and place them in a 9x13 inch baking dish.
In a separate medium bowl, combine the soup, vinegar, brown sugar and mustard powder. Mix well and pour over the meatballs.
Bake at 350 degrees for 1 hour or until internal meat temperature reaches 160 degrees F (73 degrees C).