Grease the slow cooker insert. Whisk the BBQ sauce, apple cider vinegar, brown sugar, garlic powder, onion powder, salt, and pepper in a bowl. Pour a thin layer into the slow cooker.

Nestle the chicken in a single layer and pour the remaining sauce over the top. Cover and cook on low 6 to 8 hours or high 3 to 4 hours, until the chicken shreds easily.

Transfer the chicken to a cutting board, shred with two forks, then return it to the sauce and stir to coat. Thicken uncovered on high 15 to 20 minutes if needed.

Toast the buns, pile on the hot BBQ chicken, add coleslaw if desired, and serve right away.