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A picnic or butt or boston butt which are all from the shoulder of the hog are the best cuts of pork for pulling. When you get pulled pork at your local BBQ joint it came from one or both of those cuts. Most hams are from the hind end of the hog and the aforementioned cuts are from the front shoulders. There are a few Butchers that frequent this site and one will be along shortly I am sure to more specifically tell you why.
All the picnic cuts I've ever seen are much leaner than butts. If you google, "picnic ham", there are 100's of hits for the cut used as a ham. I find the texture of the picnic roasts to much denser than a butt.
I have made picnic ham before and there is nothing wrong with it. Yum. But if you want pulled pork it works for that too. Lots of connective tissue and fat makes for good pulled pork folks.
I think it was mislabeled. And it took long because of the high internal temp you took it to. It probably only took 2 hrs or less to get to its ideal temp of 135 140. Plus less mass let's it heat up inside faster. A small piece of picnic or Boston butt would probably reach 135 140 in the same amount of time.