In a bowl, whisk together the BBQ sauce, vinegar, brown sugar, mustard, Worcestershire sauce, chili powder, garlic and thyme. Pour over the pork roast in the slow cooker. Top with the chopped onion. Cover and cook 8 to 10 hours on low.
Remove the pork from the slow cooker and shred the meat using two forks. Return the pork to the slow cooker and stir to combine the juices (if super juicy, it's okay to get rid of some of the juice).
Serve, piled on the toasted buns, with more sauce (as desired).
Notes
Nutritional information does not include buns... only the pulled pork.