In a small bowl, combine chili powder, cumin, oregano, cayenne pepper and black pepper. Rub thoroughly on the outside of the pork roast.
In the slow cooker, combine orange juice, lime juice, garlic, onion and bay leaves. Place pork on the top. Cook on low for 8 hours or high for 4-5 hours.
Remove roast from slow cooker and shred. Place on a baking sheet. Broil in the oven for 3-4 minutes to brown the edges of the pork.