In a small bowl, combine paprikas, pepper, cumin, chili powder, cayenne, garlic powder, onion powder and salt.
Pat dry the pork butt. With a sharp knife pierce the pork all over. Rub seasonings all over the pork. Making sure it is completely covered.
In a lightly greased slow cooker, whisk together Dr Pepper and barbecue sauce. Place roast in slow cooker. Cover and cook on low for 8-10 hours.(If convenient, I like to cook mine on high for 1 hour then turn down to low for 8-9 hours)
Remove pork butt from slow cooker and shred with two forks. Reserve only ¾ cup of liquid and discard the rest. Return meat to slow cooker and toss with ¾ cup cooking liquid and about ½ cup of BBQ sauce. This allows guests to add more sauce if desired with out it being dripping in sauce. Serve on rolls or buns with additional toppings such as onions, pickles, mustard etc.
Notes
Be sure that entire surface of pork butt is covered in the seasoning. I like to cook mine on high for an hour then turn down to low...this just helps the crockpot warm up quicker and start cooking.