Peel and thinly slice the onions and garlic cloves.
Place onion and garlic slices into your slow cooker.
Cover with beef broth.
Place beef roast on top of onions and garlic.
Sprinkle beef roast with garlic powder, onion powder and black pepper.
Cover and cook on low for 7-8 hours or high for 3.5-4 hours.
Remove the lid.
Turn off the slow cooker and let beef rest for 20 minutes.
Carefully remove beef from the slow cooker and place in a 9x13” pan.
Place a colander over a large bowl.
Pour remaining contents of the slow cooker into the colander, allowing the liquid to go into the bowl.
Pour the beef stock from the bowl into a quart mason jar (use 2 if needed), and place in the refrigerator.
Add the onions that are now in the colander to the pan with the beef roast.
Using 2 forks, shred the beef and combine it with the onions.