Several things are tickling my brain here, so I'll just break this down into a few sub-topics that you can think about...
For pulling meats, the finish temp is pretty crutial, with upper 190's being the minimum (for most folks here) before resting in foil/covered pan wrapped in towels. Most prefer the low/mid 200's. Be sure the probe is relatively accurate with a water boil check.
Here's some info on thermometers and a water boil-point temp chart for varied elevation/barometric pressures you can follow:
http://www.hi-tm.com/Documents/Calib-boil.html
Also, the amount of resting time for pulling meats can have a pretty drastic effect...I tried to rush a pulled shoulder once...only once...I think it was only about 45 or 60 minutes out of the smoker, and if I hadn't smoked it myself, I would have swore that it had only been taken to the 180-185* range...it was TOUGH...slicing tough, to be specific. I like to rest for at least 3 hours, with 4-5 being even more to your advantage...I'll even leave the probe in during the rest to watch the temp drop rate...if it stays above 160, you're still good to go, IMHO, and big cuts cool really slow when protected and insulated as described above...you want low & slow to cook, and low temp drop rates when it rests.
Here's another issue I had over a year ago...I had two butts, one cryovac packed in their (packer's) brine, and one which was fresh/frozen that I thawed a few days in the fridge prior to smoking. The fresh butt would not pull, no way, no how. The cryovac packed was a dream...both smoked side by side and pulled to foil and bring to finish temps at 180* and pulled to wrap and rest @ 205*. I never would have guessed that brining would have such a huge impact on the tenderness of the finished product, but it did.
I guess this is the question I have: Was this butt fresh with no brine, fresh that you brined yourself, or was it cryovac packed?
Eric