ya i made a shoulder this weekend. same thing.
its not the foil. i still get nice crispy bark on top and sides. the thing is when you buy the shoulder, on the bottom is actual pig skin. when you cook that side down in the foil, it just stays nasty gooey skin. mine did the same. thats why i like making butts better.
20x48 Pits by JJ
Cinder block smoker