Pulled Pork (Slow Cooker): Pat pork dry and rub with brown sugar, smoked paprika, chili powder, salt, pepper, and cumin. Place sliced onions and garlic in the slow cooker. Add seasoned pork on top. Pour in BBQ sauce and chicken broth. Cover and cook on LOW for 8 hours (or HIGH 4–5 hours) until pork is tender and shreds easily. Remove pork and shred using two forks. Return to slow cooker and mix with juices. Keep warm.
Mac and Cheese: Cook pasta in salted boiling water until al dente. Drain and set aside. Melt butter in a saucepan over medium heat. Whisk in flour and cook for 2 minutes to form a roux. Gradually whisk in milk, stirring until thickened. Stir in cheddar, mozzarella, and Parmesan until melted and creamy. Season with mustard powder, salt, and pepper. Combine pasta with cheese sauce until fully coated.