1. Mix together brown sugar, paprika, salt, black pepper, garlic powder, and onion powder in a bowl.
2. Rub the spice mixture all over the ribs.
3. Place the ribs in the slow cooker, meat-side up.
4. Pour BBQ sauce over the ribs.
5. Cover and cook on low for 8 hours.
6. Preheat oven to 375°F (190°C).
7. Carefully remove the ribs from the slow cooker and place them on a baking sheet lined with aluminum foil.
8. Brush additional BBQ sauce over the ribs.
9. Bake in the preheated oven for 10-15 minutes, until the sauce is caramelized.
10. Let the ribs rest for a few minutes before serving.