Remove the silver skin membrane from the back of the ribs, and cut into smaller sections that will fit into the slow cooker.
In a small bowl, combine the salt, pepper, paprika, garlic powder, onion powder, and chili powder.
Coat both sides of the ribs with the seasoning.
Place the ribs in the slow cooker, lining them up on the edges if you can.
Combine the BBQ sauce, brown sugar, apple cider vinegar, Worcestershire sauce, and Dijon mustard in a separate bowl.
Pour the BBQ sauce over the ribs in the slow cooker.
Cover and cook on LOW for 6-8 hours (HIGH for 3-4 hours), until the meat is very tender.
Preheat the oven to 425°F (220°C), and line a baking sheet with foil.
Transfer the ribs to the baking sheet, and brush with additional BBQ sauce.
Broil for 5-10 minutes, until the BBQ sauce is caramelized and sticky. Let cool slightly before serving.