Melt 2 tablespoons of the butter in either the slow cooker insert (over a hot stovetop) or in a large, heavy-bottomed skillet.
Add the salt, chili powder, cumin, garlic powder, and pepper to a large bowl and stir to combine. Add the pork to the bowl and toss to coat with the seasoning.
Once the butter is melted and starting to bubble, add the pork to the skillet, working in batches if needed to make sure you don't overcrowd the pan. Sear pork on all sides for about 4 minutes over high heat, or until a brown crust starts to form (but before it burns).
Transfer the pork to the slow cooker, then pour the orange juice over the pork. Cover and cook on low for 8 hours or on high for 4 hours, until the pork easily shreds with a fork.
Once the timer goes off, use two forks to shred the pork into 1-inch pieces.
Preheat the oven to 425°F.
Transfer the pork to a rimmed baking sheet, then toss the pork with the melted butter and lime juice and spread it out onto a rimmed baking sheet. Bake at 425°F for 15 to 20 minutes, or until the tops are starting to look a little crispy.
Assemble the tacos with the carnitas, cilantro, lime wedges, flaky sea salt, and serve!