Line a 6–7 quart slow cooker with foil or a crock pot liner.
Evenly layer the sliced onions on the bottom of the slow cooker.
Place the pork shoulder on top of the onions and pour the Dr Pepper over the meat.
In a small bowl, mix liquid smoke, honey, and minced garlic. Use a basting brush to evenly coat the pork with this mixture.
In another bowl, combine the brown sugar, onion powder, salt, smoked paprika, black pepper, and cumin. Sprinkle evenly over the pork.
Cover and cook on HIGH for 4 hours or LOW for 6 hours, until the pork is tender and easily shreds.
Shred the pork with forks or tongs directly in the slow cooker or transfer to a large dish to shred.
Pour BBQ sauce over the shredded pork and toss until evenly coated.
Serve warm on hamburger buns or deli rolls, optionally topped with coleslaw.
