In a small bowl, mix together the brown sugar, paprika, salt, black pepper, garlic powder, and onion powder to create a dry rub.
Rub the mixture all over the pork shoulder, covering it completely.
Place the pork in a slow cooker and pour the barbecue sauce over the top.
Cover and cook on low for 8 hours, or until the meat is tender and easily shreds with a fork.
Remove the pork from the slow cooker, shred it with two forks, and return it to the sauce. Stir to combine.
Serve hot on buns, with additional barbecue sauce if desired.