Layer the chicken: Place chicken in the bottom of the slow cooker in a single layer. If using large breasts, cut them in half for even cooking.
Make the gravy base: In a bowl, whisk together cream soups, chicken broth, gravy packets, onion powder, garlic powder, and black pepper until smooth.
Assemble: Pour the gravy mixture over the chicken.
Dot the top with butter if using.
Cook low and slow: Cover and cook on Low for 4–6 hours or on High for 2.5–3.5 hours, until the chicken is cooked through and easily shreds.
Shred and enrich: Remove the chicken to a plate and shred with two forks. Stir sour cream or Greek yogurt into the gravy, then return the chicken and mix to coat.
Taste and adjust: Add salt only if needed. Gravy packets can be salty, so season at the end.
Serve: Spoon the chicken and gravy over mashed potatoes, rice, or noodles.
Garnish with parsley for a fresh finish.