Place garlic, onion, vinegar, oil and seasonings in blender container. Cover. Blend on high speed until smooth. Place pork in large roasting pan. Using a sharp knife, make deep slits all over pork. Rub seasoning mixture all over pork, pressing into slits. Arrange pork roast, skin side up, in pan. Cover pan with foil.
Refrigerate 8 hours or overnight for extra flavor. After refrigerating, pour 1/2 cup water into pan. Cover pan with foil.
Preheat oven to 350°F. Roast pork 4 hours or until very tender, removing foil halfway through cook time.