Rinse roast under cold running water and pat dry with paper towels.
Season roast with a little salt and pepper.
Heat vegetable oil in a large deep sided pot over medium heat.
Brown the roast on all sides until golden brown. Once the roast is nicely browned, transfer the roast to a slow cooker.
Top the roast with the pepperoncini slices and juice.
Top peppers with minced garlic.
Sprinkle ranch and au jus seasonings over the top.
Finally, top everything in the slow cooker with pats of butter.
Cover and cook on low for 7 to 8 hours., or until meat is tender and shreds easily.
To serve, shred the meat with two forks and serve over a bed of mashed potatoes. Ladle some of the gravy in the bottom of the slow cooker over the meat and potatoes.