Place pork roast in slow cooker. Add paprika, onion powder, salt and pepper. Place the onion around the roast. Pour beef stock over pork and turn to high heat for 6 hours.
For bbq sauce:
Meanwhile, mix the ketchup, broth from pulled pork, both sugars, 1 1/2 teaspoons pepper, the onion and mustard powders, lemon juice, Worcestershire sauce, vinegar, corn syrup and in a saucepan over high heat. Bring to a boil, stirring, then reduce the heat to low and simmer, uncovered, stirring occasionally, for about 15 minutes. Once thickened remove from heat and set aside. Drain most of remaining juice from pulled pork and shred with forks(I leave about 1/2 cup) then pour bbq sauce into the slow cooker and turn heat to low. Stir the pork and bbq mixture to coat the meat. Cook on low heat for about 30 minutes.
To make sandwiches top buns with pulled pork and coleslaw of your choice.