Combined Apple Juice, 1 cup vinegar and 1 cup pepper jelly in a saucepan over medium heat. Stir together until jelly melts. Place pork in large sealable bag and pour marinade over. Seal bag and marinate in refrigerator 12 to 24 hours. Prepare covered grill with banked coals. Remove pork from marinade. Reserve marinade. Place pork roast over drip pan and cover grill. Grill about 1¼ hours or until meat thermometer reads 150º, basting occasionally with reserved marinade. Combine ¼ cup vinegar and ¾ cup pepper jelly in a bowl. Coat roast with jelly glaze for last 10 minutes of grilling. Continue to cook until a meat thermometer reads 160º. Let rest 10 to 15 minutes before slicing.