Cut meat in half. Place meat in a roasting pan and put in a 300-degree oven. Sprinkle with garlic, five spice, and sugar. Add soy sauce and 1 cup water.
Cover and cook until pork is very tender when pierced, about 3 to 4 hours. Bake uncovered 450 degrees until well browned, 15 to 20 minutes. Using 2 forks, shred meat; discard bones and fat. Put meat in a bowl, cover, and keep warm.
Skim and discard fat from cooking liquid; pour into a 2 to 3-quart pan. Add vinegar. Bring to a boil, stirring often, until reduced to 1 cup, about 15 minutes. Add hoisin.
Warm tortillas. Pour reduced sauce over shredded pork. Spoon some of the meat onto a warm tortilla; top with cabbage, onions, and cilantro. Fold 1 end of tortilla over filling, overlap sides to enclose, and hold shut to eat. Serves 6 to 8.