Season the beef chuck roast with salt and pepper.
Place the roast in the slow cooker.
Sprinkle the ranch dressing mix over the roast.
Add the au jus gravy mix on top.
Scatter the sliced onion around the roast.
Place the pepperoncini peppers on top of the roast.
Pour the beef broth into the slow cooker.
Cover and set the slow cooker to low for 8 hours.
Once cooked, shred the meat using two forks.
Serve with the juices from the slow cooker.