Combine the spice mix together in a small bowl. Pat pork (3-5 pound) dry with paper towels and rub spice mix into the surface, making sure all 3 pieces are evenly coated.
Turn IP to saute and add 2 tablespoons of oil. Once shimmering, sear pork, 1 piece at a time, until golden on each side - should take about 3-4 minutes per side. Set seared pork aside on a plate, and repeat with 2 remaining pieces. Make sure to add more oil as needed, I usually use 4 tablespoons in total. Once pork is cooked, press cancel on the IP (it should be very hot at this point). Add balsamic (2 tablespoons) to the pan and scrape up brown bits using the back of a wooden spoon.
Nestle the trivet inside the IP, and add broth (1 cup). Place the pork on top, and any accumulated juices from the plate. Add the lid, making sure the pressure release valve is set to sealing. Set IP to high pressure for 60 minutes. Once done cooking, turn the pressure release to venting. Remove the lid once the pin has dropped.
Remove meat to a plate. Add veggies and seal once more. Cook on high pressure for 4 minutes. Once cooked, turn pressure release to venting, and when the pin drops, remove the lid. Use a slotted spoon to grab all the veggies, and place them on the plate with the meat.
While the veggies are cooking, shred the pork with 2 forks, then loosely cover with foil to keep warm.
Turn IP to saute. If using cornstarch (2 tablespoons), dissolve it in a small bowl with the heavy cream (1/4 cup), then pour it into the cooking liquid. If using xanthan gum (1/2 teaspoon), add heavy cream to the IP, then lightly sprinkle cooking liquid with xanthan gum and whisk immediately (NOTE: xanthan gum will clump easily, so you'll want to work quickly here.) Continue to simmer until the gravy has thickened to your liking, should take 3-4 minutes. Taste and adjust the salt to your liking -- I usually add 1/2 teaspoon of additional salt to the gravy at this point.
Drizzle gravy over pork and veggies. Sprinkle with chopped parsley and enjoy!