Place the chuck roast flat in the slow cooker insert. Do not add liquid.
Sprinkle the ranch seasoning packet evenly over the top of the roast, then follow with the au jus packet.
Place the butter on top of the seasoned roast. Arrange the pepperoncini peppers around and over the beef, then pour the brine over the top. Put the lid on.
Cook on LOW for 8 hours. The roast is done when it shreds easily with two forks and the internal temperature reads 93°C to 98°C (200°F to 210°F).
Shred the beef with two forks directly in the slow cooker. Discard any large pieces of solid fat. Stir the shredded beef through the gravy.
Rest with the lid off for 10 minutes before serving.