Mix together the chili powder, cumin, garlic powder, and brown sugar. Rub it all over the pork shoulder. Sear the pork shoulder in a large pan/pot until golden brown on both sides.
Mix together the orange juice and lipton onion soup mix in a bowl. Place the the pork shoulder into the slow cooker and pour the orange juice and onion mix over it and into the slow cooker.
Set the slow cooker on high for the first hour and then set to low for the remaining 8 hours (or until fork tender). Shred the meat and serve.
Notes
Serve with a fresh salsa and chopped avocado, or on a warm soft taco filled with your favorite toppings.