In a blender or food processor, combine the ketchup, chipotle chilis, ½ c red wine vinegar, dijon mustard, brown sugar, maple syrup, Worcestershire sauce, black pepper, and garlic. Blend until smooth, and set aside.
To cook the pork:
Pour the oil into the bottom of the slow cooker, then add the onions and pork shoulder and season with a generous pinch of salt. Pour in the chicken broth, water, and barbecue sauce. Cover the roast and cook on high until the meat falls apart easily—about 6 hours.
When the meat is tender, carefully remove from the slow cooker and shred in a large bowl or on a large rimmed baking sheet with two forks, or your hands if the meat is not too hot. Remove any excess fat and reserve juices that come out. Using a slotted spoon, strain about ½ c of the onions and solids from bottom of the slow cooker (drain off the excess fat on top) and add to the meat. Drizzle with the remaining 2 Tbsp of vinegar and mix until combined.
Serve hot on slider buns with cold, crisp, coleslaw, vinegary pickles, and fresh lime juice! Or in tacos, enchiladas, burritos, taco bowls, nachos, etc.