Add all ingredients to pot. Set to Pressure Cook for 30 minutes. Release pressure naturally for 15 minutes.
Release any remaining pressure manually. Remove meat from pot and shred with 2 forks.
Serve on a tortilla with toppings of your choice, such as cheese, lettuce, cilantro, sour cream, avocado, etc., or serve on top of a salad.
I was not successful at deboning my butt roast, so I had a chunk of meat with the bone that weighed about 2 1/2 lbs. and was still partially frozen. It took about 1 hour to cook this way, but it was absolutely fantastic!