Rub the pork shoulder with vegetable oil and rub generously with your choice of dry rub seasoning on all sides. Place into a large mixing bowl. Cover tightly with plastic wrap, and refrigerate overnight.
When you're ready to prepare the pork shoulder, spray the inside of the slow cooker with cooking spray and set it on the low setting.
Mix the Dr. Pepper with the liquid smoke and pour it into the bottom of the slow cooker.
Center the pork shoulder in the cooking liquid.
Cook on the low setting for 9-10 hours.
After the shoulder has finished cooking, remove it from the slow cooker and discard the cooking juices.
Shred the pork with a fork, removing any visible fat, then place the pulled pork back into the slow cooker and increase the temperature to the high setting.
Pour 2 1/2-3 cup of barbecue sauce on top. This can be your favorite homemade or prepared sauce.
Cook on high for 45-50 minutes just long enough for the sauce to simmer into the pork.
Serve on kaiser rolls with cole slaw and extra sauce on the side.
If you'd like to take a shortcut for the sauce, I recommend using any prepared sauce with a chipotle flavor to reflect the flavors in the dry rub.