Season pork shoulder with salt and pepper to taste. Place in slow cooker.
Mix together salt, pepper, paprika, garlic powder, onion powder, dry mustard, ketchup, vinegar, brown sugar, Worcestershire sauce, prepared mustard, and chili powder. Reserve about 1/2 cup sauce, set aside. Pour remaining sauce over pork and cook on low 6-8 hours.
Mix together broccoli slaw, prepared mustard, white vinegar, mayonnaise, sugar, red pepper flakes, chili powder, and salt. Add red onions and toss to combine. Chill until ready to serve.
About 30 minutes before serving, shred pork with two forks. When ready to serve, stuff each pita pocket with about 1/2 cup shredded pork and 1/3 cup slaw. Drizzle with reserved barbecue sauce.