You said shoulders, are these "whole shoulder" that include the butt? .. Or, shoulder as in "Picnic ham"? If these include the butt, I would separate and cook for pulled pork. Otherwise, the picnics have the skin on it. So Rubs are not going to penetrate the meat well. Maybe a light injection solution (pepper & garlic; very little salt). I would leave the skin on to hold moisture in during the long cooking. .... Next, how are these going to be served? Pulled, falling apart or sliced? .... Pulled or falling apart, I would cook to 180/190 deg. For sliced, cook to 160/170 deg. Let the customer add BBQ sauce to their plate. ... Work on a kick-ass sauce!!!!