Spray crock pot with cooking spray, and lay roast beef inside.
Sprinkle au jus mix and ranch seasoning over beef.
Toss in peperoncini, split butter into chunks and sprinkle across seasoning.
Return lid to crock pot and cook on high for 4 to 5 hours or on low for 8 to 9 hours. Allow roast to rest for 10 minutes before slicing, and serve with pan juices.
The roast will fall apart easily; shredded, it is ideal in tacos and on sandwiches.