Lightly grease the slow cooker with nonstick cooking spray.
Place the chicken breasts in the bottom of the slow cooker.
Sprinkle the ranch seasoning and brown gravy mix evenly over the chicken.
Pour the barbecue sauce over the top.
Add the sliced pepperoncini peppers and pepperoncini juice.
Arrange the butter slices over the chicken.
Cover and cook on LOW for 6–7 hours or HIGH for 3–4 hours, until the chicken is tender and easily shreds.
Shred the chicken directly in the slow cooker using two forks, stirring it into the flavorful sauce.
Sprinkle the shredded cheddar cheese evenly over the chicken.
Cover for 5–10 minutes, or until the cheese has fully melted.
Garnish with chopped parsley if desired and serve warm.