Sprinkle the roast pieces liberally with salt and pepper on all sides. Use the saute mode to heat the olive oil in the instant pot insert. Add the pieces of roast to the pot and cook for 3-4 minutes per side, until browned (you may need to do this in two batches).
Remove the roast to a plate and add the onion to the pot. Cook, stirring frequently, until softened. Add the garlic to the pot and cook 2-3 minutes, until fragrant.
Add the balsamic vinegar and Worcestershire sauce to the pot and scrape up the browned bits from the bottom of the pot.
Return the roast to the pot and pour the beef broth over the top. Add the lid to the pot and turn the knob to seal. Cook for 45 minutes on the meat/stew setting, then let the pressure naturally release for 20 minutes. Quick release the remaining pressure.
Add the potatoes and carrots to the pot, cover, and turn the knob to seal.
Cook for 8 minutes on high pressure, then let the pressure naturally release for 10 minutes. Quick release the remaining pressure.
Move the roast and vegetables to a serving platter, shred the roast (if desired), and cover with foil.
Pour the broth from the pot through a strainer into a skillet and heat over medium heat.
In a small bowl, whisk together the corn starch and water, and pour the cornstarch slurry into the broth. Bring the gravy to a simmer and simmer until thickened. Pour the gravy over the roast and vegetables.