Place the pork butt in a half pan or on a large prep surface. Using a sharp knife, score the fat cap and surface of the pork so the seasoning can get down into the meat.
Season the pork generously on all sides with barbecue rub. Work the seasoning into the scored areas and make sure the pork is fully coated. Let it sit for about 30 minutes so the seasoning can begin to sweat into the meat.
Fill your pellet smoker with pecan pellets and preheat it to 225°F. Place the pork shoulder on the smoker. You can cook it directly on the grates or place it in a half pan to catch the rendered juices.
moke the pork low and slow at 225°F for about 12 hours. Keep the lid closed as much as possible so the smoke and heat stay steady.
After about 12 hours, check the pork for tenderness. If it needs more time, raise the smoker to 275°F and continue cooking until the meat is probe tender. The probe should slide into the pork with very little resistance.
Remove the pork from the smoker and let it rest for 30–45 minutes. Cover it loosely with foil while it rests. If it is still too hot to handle, let it cool a little longer before pulling.
Remove the bone from the pork. It should pull out clean when the pork is fully cooked. Shred the meat, mixing the bark into the pulled pork so every bite has smoky flavor.
Add a little reserved pork drippings or rendered fat back into the meat to keep it juicy. Drizzle in barbecue sauce a little at a time and toss until lightly coated. Serve on buns with coleslaw or as part of a barbecue plate.