In a small bowl, mix the rub ingredients (brown sugar, paprika, garlic powder, onion powder, cumin, salt, and pepper).
Rub spice mix onto both sides of the chicken breasts. Set aside.
Stir BBQ sauce ingredients together in the slow cooker. Layer the seasoned chicken breasts into the slow cooker.
Slow cook chicken for 4 hours on high, or 6 hours on low.
When finished cooking, remove chicken from the slow cooker and shred each breast. Place chicken back in the crock pot, stir with the BBQ sauce, and keep cooking for 10 minutes.