Trim and discard excess fat from the pork.
In a small bowl, combine chili powder, cumin, oregano, salt and pepper. Generously season the pork on all sides.
Add the seasoned pork to the bottom of the instant pot. Add garlic, onions, orange juice and lime juice.
Cook on Manual/High pressure for 45 minutes. When timer beeps, allow the pot to naturally release pressure, about 15 minutes longer. Remove lid and shred the meat.
For a more authentic taste, place the meat on a baking sheet and broil it for 2-3 minutes until the edges are crispy.