Rub pork butt generously with a prepared dry rub seasoning on all sides. i.e. Barbecue Magic, McCormicks Smokehouse or similar. (See Cook's note for homemade.) Wrap with plastic wrap, and refrigerate overnight.
Prepare: Spray the crock of a 6 quart slow cooker with cooking spray.
Mix Dr Pepper with the liquid smoke. Pour into slow cooker. Center the pork shoulder in the cooking liquid.
Cover and cook on the low for 8-10 hours until fork tender.
Remove pork to a platter. Discard the cooking juices.
Shred pork using 2 forks, removing any visible fat. Return pulled pork back to the slow cooker. Increase the temperature to high.
Pour 2 cups barbecue sauce over pork. Cover and simmer 30-45 minutes just until sauce has simmered into pork.
Serve on kaiser rolls or buns with coleslaw and extra sauce on the side.
Notes
If you'd like to take a shortcut for the sauce, I recommend using a bottled barbecue sauce with a chipotle flavor to reflect the flavors in the dry rub such as Sweet Baby Rays.Homemade rub: