Mix garlic, brown sugar and salt together and coat the outside of the roast on all sides. Place a trivet into your pot + 1.5 cups water underneath.
Set meat on top of trivet, close lid and seal steam valve closed. Cook on high pressure for 50 minutes with a 10 minute natural release. Then release rest of steam.
Lift out and slice. You can make gravy out of the drippings by removing the trivet and turning pot to saute. Spoon 4 tbsp of your hot liquid into a small cup + 1 tbsp of cornstarch. Whisk until smooth and then pour that in. Whisk contents as it boils until it thickens, then turn pot off.
If you want to create a crust on the outside you can place on a foil lined baking sheet. Set oven to broil and put it in there for 2-3 minutes just until outside browns. You could add more of the dry rub beforehand to make it thicker and caramelized all the way around.