1 teaspoon vegetable oil 1 (4 pound) pork shoulder roast 1 cup barbecue sauce ½ cup apple cider vinegar ½ cup chicken broth ¼ cup light brown sugar 1 tablespoon prepared yellow mustard 1 tablespoon Worcestershire sauce 1 tablespoon chili powder 1 extra large onion, chopped 2 large cloves garlic, crushed 1 ½ teaspoons dried thyme 8 hamburger buns, split 2 tablespoons butter, or as needed Pour vegetable oil into the bottom of a slow cooker. Place pork roast into the slow…