I looked at your whole process. I could be wrong but it was overdone for 2 reasons. 16 1/2 hours is way too long for that cut. I would bump up the temp and get it done sooner. Second madman mentioned it, were you going for a "roast" or more like a pulled pork. If so you still cooked too long for roast and not high enough internal temp for the pulled style you have had success in the past with.
Taylor-WSM 18.5 with Wifi Stoker, Kamado Smoker BBQ, and lots of charcoal. 180 club-Chicken