The general rule around here is that you cook your meat until the correct internal temperature of the meat is reached, versus cooking for a set period of time. Do you have a meat thermometer? For pork to pull easily it should hit an internal temperature of 200 - 205 deg F. Then cover it with foil and let it rest for an hour or so before pulling. Most folks here will monitor both the chamber temperature as well as the meat internal temperature; I use the Maverick ET-732 for this, although there are many other options out there. How big was your pork butt? It is not unusual for pork butts to take 12, 16, or even 20 hours to reach the correct internal temperature.
I would guess that your pork butt was only cooked to around 180 or 190 deg F. It is fully cooked and tasty, but has to be sliced because the collagen hasn't broken down enough to permit for easy pulling.
I'm sure others will be around to give their opinions as well. Welcome to SMF, and I'm sure you'll have a great time and learn a lot here!
I'm giving your question a little bump to try and get you more responses. Also, a reason you aren't getting more responses is that you posted your question in the Washington Smoker Group, which means only people that are enrolled in that group can reply back to you. In future, if you post questions to a general forum like Forums > Smoking Meat (and other things) > Pork, then everybody can reply back to you, and you will get more help quicker.
It takes a moderator to move your question, otherwise I'd do it for you.
Good luck, and I'm sure your next butt will be great!