Combine enough apple juice, Worcestershire sauce, and molasses (or maple syrup) [all to taste] to marinate pork shoulder (plus 1-2 cups reserved). Marinate for 2-3 hours [or, inject the marinade into the pork]. Pat dry and coat with a thin coating of prepared mustard and then liberally coat all sides of the pork shoulder with rub. Rest for about one hour to allow meat to approach room temperature and rub to begin to flavor the pork.
Preheat pellet smoker/grill to 180º; place pork shoulder on grill, fat side down. When pork shoulder reaches an internal temperature of approximately 160º, tightly wrap in foil after adding a small amount of the apple juice marinade. Increase the heat of the pellet grill to 225º. Cook until internal temperature of pork shoulder reaches 195-200º. Remove from grill and place in an insulated container for 30 plus minutes. Shred pork shoulder and serve with rolls and coleslaw.
(Note: You can also finish the foil wrapped pork in an oven preheated to 225º until the internal temperature of 195-200º is reached and continue as outlined above.)