Combine all dry rub ingredients in a small bowl and mix well.
Pat pork dry with paper towels. Coat the entire surface with yellow mustard, then press the dry rub firmly into all sides until fully covered.
Pour apple cider vinegar and chicken broth into the slow cooker. Place pork fat-side up.
Cover and cook on LOW for 8 to 10 hours or HIGH for 5 to 6 hours until the meat is fork-tender and pulls apart easily.
Transfer pork to a cutting board. Remove the bone and any large fat pieces. Shred using two forks.
Return shredded pork to the slow cooker. Add BBQ sauce and stir to coat. Cook on LOW an additional 20 to 30 minutes to absorb the sauce.
Serve on toasted buns.