Cut the pork butt into 4 equal-sized pieces. Add to the slow cooker.
In a mixing bowl, add the orange juice, lime juice, salt, cumin, oregano and garlic. Mix to make a sauce.
Pour the sauce over the pork. Cover and cook on low for 6-8 hours until tender.
For optional crisping of the pork, transfer the cooked pork to a sheet pan. Turn oven to broil (high). Shred pork with two forks and spread it out across the sheet pan. Take 1/4 cup of the sauce from the slow cooker and sprinkle it over the pork.
Transfer to the oven and broil about 5 minutes or until the tops of the pork start to turn brown and crispy. Serve immediately.