OPTIONAL: Turn your instant pot to saute and add in oil. Season pork roast liberally with the kosher salt. When Instant Pot reads "Hot," add pork loin to instant pot and sear until browned on each side. (Skip if you are in a time crunch or using a frozen pork roast.)
Mix together orange juice, stock, cumin, oregano and garlic powder and pour over pork loin.
Seal pressure cooker and be sure vent is pointing to "sealed." Set pressure to high and cook for 20 minutes per pound (60 minutes for 3 pounds or 80 minutes for 4 pounds.)
Once cook time has elapsed, let pressure release naturally.
Shred pork with 2 forks or kitchen mixer (stand or hand-held mixer both work.)
If you want to crisp the edges of the shredded pork, place meat on rimmed sheet pan with 1/2 cup cooking liquid and broil under high heat for 3-5 minutes per side.
Serve Mexican pork with tortillas and shredded cheese, over rice, or over baked potatoes.