Place the chicken breasts in the base of the slow cooker.
Evenly distribute the au jus mix and ranch seasoning over the chicken. Arrange the butter pats and pepperoncini on top.
Cook on LOW for 3 hours or on HIGH for 1.5 to 2 hours. Use a thermometer to ensure the internal temperature of the chicken reaches 165°F (75°C).
Allow the chicken to rest for 5 minutes before shredding it while warm using two forks, a hand mixer, or your hands.
Serve the chicken atop mashed potatoes, pasta, or rice. For sandwiches, layer it on rolls or toasted buns with provolone cheese.