Season both sides of the roast lightly with kosher salt and ground black pepper.
In a large skillet over medium-high heat, heat vegetable oil until shimmering. Add the roast and sear for about 2–3 minutes on each side, until a golden crust forms.
Transfer the seared roast to the slow cooker.
Sprinkle ranch dressing mix and au jus gravy mix evenly over the top of the roast.
Place the sliced butter on top of the seasonings.
Add whole pepperoncini peppers around and on top of the roast. Pour pepperoncini juice over everything.
Cover and cook on low for 8 hours, or until the meat is fall-apart tender and easily shredded with a fork.
Shred the meat in the slow cooker using two forks, mix gently to coat with the juices, and serve warm over mashed potatoes, rice, or noodles.