In a small bowl, mix the brown sugar, paprika, chili powder, cumin, garlic powder, onion powder, salt, and black pepper.
Trim the fat from pork roast and cut into four chunks. Rub the spice mixture over all sides of the pork.
Set the Instant Pot to 'Sauté' mode and add the vegetable oil.
Once hot, add and sear pork pieces for 2-3 minutes per side. Cook in batches if needed.
Turn off 'Sauté' mode. Remove the pork and set it aside.
Pour the chicken broth, Worcestershire sauce, and liquid smoke into the pot. Stir, scraping up any browned bits from the bottom.
Return the pork to the pot.
Secure the lid and set the Instant Pot to cook on high pressure for 75 minutes.
When the cooking time is up, let the pressure release naturally for 20 minutes, then carefully release any remaining pressure.
Remove the pork from the pot and shred it using two forks. Mix in the BBQ sauce.
If desired, mix the shredded pork with some of the cooking liquid or extra barbecue sauce.
Serve the pulled pork on buns with your favorite sides.