Lightly grease the slow cooker with cooking spray.
Place the chicken breasts in the bottom of the slow cooker.
Sprinkle the chicken with garlic powder, onion powder, thyme, parsley, salt, and black pepper.
In a medium bowl, whisk together the cream of chicken soup, chicken broth, and gravy mix until smooth.
Pour the gravy mixture evenly over the chicken.
Dot the top with butter.
Cover and cook on LOW for 5 to 6 hours or HIGH for 2½ to 3 hours, until the chicken is tender and reaches an internal temperature of 165°F (74°C).
Remove the chicken and shred it with two forks, or leave it whole if preferred.
Stir the sour cream into the gravy until smooth.
Return the chicken to the slow cooker and stir to coat it in the creamy gravy.
Cook for another 10 to 15 minutes on LOW.
Serve over mashed potatoes, rice, noodles, or biscuits and garnish with fresh parsley.