Trim the beef roast and cut into large chunks, discarding any large pieces of fat. Pat dry and set aside.
In a small bowl, combine the garlic powder, onion powder, salt and pepper. In a large bowl, sprinkle over the chunks of beef, covering evenly.
Heat the olive oil in a large skillet. Brown all sides of the beef chunks, approximately 2 minutes per side.
Coat the inside of a large slow cooker with olive oil or cooking spray. Transfer the browned beef to the pot.
Vegetable Trimmings:
Top the beef with the tomatoes, onion, carrots, mushrooms and potatoes.
Sauce:
In a large bowl or measuring cup, whisk together the beef broth, vinegar, brown sugar and mustard until the sugar has dissolved. There might some bits of mustard and that is fine.
Pour over the beef and vegetables.
Cook the Roast:
Place on the cover and set to 8 hours on low or 4 hours on high. Pot roasts do best low and slow so I highly recommend the 8 hour option. Occasionally spoon sauce over the beef and turn the beef chunks.
Just before you are ready to serve, remove the beef and vegetable trimmings using a slotted spoon. If desired, shredded the beef using two forks.
Carefully pour the sauce through a fine mesh sieve into a saucepan. Discard solids.
In a small bowl, whisk together 2 tablespoons of water with 1 tablespoon of cornstarch. Whisk it back into the sauce and bring to a low simmer, continuing to whisk until it thickens and turns glossy.
Spoon the sauce over the beef and vegetables and serve.
If you've tried this recipe, come back and let us know how it was in the comments or star ratings.
Notes
To Make in the Instant Pot: Saute the beef directly in the pot. Add the vegetables and sauce to the pot. Close and lock the lid and vent. Cook on high pressure for 35 minutes, allowing for 10 minutes of natural release. Follow the same instructions for serving and thickening the sauce.