In a mixing bowl, whisk together the gravy mix, cream of chicken soup, water, garlic powder, and black pepper until smooth.
Place chicken breasts in the crock pot and pour the gravy mixture over the top.
Cover and cook on LOW for 6-8 hours or on HIGH for 3-4 hours, until chicken is tender.
Shred the chicken in the crock pot and stir in the sour cream until fully combined and smooth.
Serve hot over mashed potatoes, rice, or your favorite side.