Season roast with salt and pepper and place in bottom of slow cooker.
Top with onion and garlic.
Pour over the bottle of BBQ sauce.
Cover and continue to cook on low** for 6-7 hours. Shred meat with fork and stir back into sauce. Cover again and cook one more hour before serving. Pile filling into rolls.
**If you prefer to cook beef on high, do so for 4-5 hours and then shred. Cook another hour.
Notes
Because this recipe takes about 7 hours to make, it's perfect to start in the morning and it will be ready when you get home.