Sear the roast in a heavily oiled, hot cast iron skillet until browned on each side (about 2 min per side).
Transfer to the slow cooker. Pour the special sauce all over the meat.
Cook on low with the lid on for about 6 hours.
Take the meat out of the slow cooker and shred it all up. Place in a serving dish or other container, and pour about 1/4 of the liquid from the slow cooker over the beef.
Serve the beef with tortillas, cilantro, and your favorite salsa and make tacos, or use it in a burrito bowl with rice, black beans, and your favorite toppings.