Preheat oven to 325 degrees F. Trim the excess fat from the pork butt. In a small bowl, mix together the pepper, kosher salt, cumin, thyme, sage, chili powder, paprika, mustard, and garlic powder. Rub the pork with an even coating of the seasoning mix.

In a heavy ovenproof pot or small Dutch oven (the pork should fit snugly in the pan), heat the oil. Sear the meat over medium heat, browning well on all sides, about 4 minutes per side. Add the root beer (the liquid should come about 1/3 of the way up the meat), and cover the pot with a lid.

Place the pot in the oven and bake for 1 hour, then turn the meat over. Cover and continue baking until the meat is tender enough to shred, about 1 more hour.

Remove the pot from the oven. In a large bowl, shred the pork using 2 forks (you should have about 4 cups of shredded meat). Skim the fat from the pan juices, and stir in the pork and barbecue sauce. Place the pan uncovered in the oven, and bake for about 30 minutes, until the juices thicken. Serve immediately.