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You need to get the IT up around 200* for it to be pulled. My guess is you didn't get near that in only 6 hrs. You should plan between 1.5-2 hrs per Lb.
The shoulder has the butt and the picnic. IMHO the butt is the best for pulled pork for a manageable size. For a group the whole shoulder pulled and mixed together is great too.
And yes... you need to get to minimum 195 to 200 IT.