In a small bowl, combine brown sugar, smoked paprika, garlic powder, onion powder, chili powder, cumin, salt, black pepper, and cayenne. Mix well to create the spice rub.

Pat the pork shoulder completely dry with paper towels. Generously coat all sides of the pork with the spice rub, pressing it into the meat. Let sit at room temperature for 15 minutes.

Heat vegetable oil in a large skillet over medium-high heat. Sear the seasoned pork shoulder on all sides until deeply browned, about 3-4 minutes per side. This creates crucial flavor development.

Transfer the seared pork to your crockpot. In a small bowl, whisk together apple cider vinegar, barbecue sauce, and chicken broth.

Pour the liquid mixture around (not over) the pork in the crockpot. Cover and cook on LOW for 8-10 hours, or until the pork easily shreds with a fork.

Carefully remove the pork from the crockpot and let rest for 15 minutes. Meanwhile, pour the cooking liquid through a fine-mesh strainer into a small saucepan.

Bring the strained liquid to a boil over high heat and reduce by half, about 10-15 minutes, until thickened and glossy. Season with salt and pepper to taste.

Shred the pork using two forks, discarding any large pieces of fat. Toss the shredded pork with enough of the reduced cooking liquid to moisten. Serve immediately with additional barbecue sauce on the side.