In a slow cooker, combine the chuck roast, pepperoncini, pepperoncini juice, unsalted butter, au jus mix, ranch dressing mix, salt, and pepper.
Cover and cook on Low for approximately 8 hours or until the roast is fork-tender.
Once cooked, remove any large chunks of fat from the roast and shred the meat using forks.
To assemble the sandwiches, place a generous amount of shredded beef onto each bun.
Top the beef with a slice of Provolone cheese and cooked pepperoncini, if desired.
Spread horseradish sauce or mayo on the top bun before placing it on top of the sandwich.
Serve the sandwiches hot and enjoy the burst of flavors with every bite!