Lightly grease the slow cooker insert and arrange the chicken breasts in a single layer.
Stir the condensed cream of chicken soup and sour cream until smooth, then spread the mixture evenly over the chicken.
Sprinkle the dry stuffing mix across the creamy layer. Do not stir; keep the stuffing on top.
Cover and cook on LOW for 4 to 6 hours. Begin checking at 4 hours and stop when the thickest part of each chicken breast reaches 165°F (74°C).
Spoon the stuffing and creamy sauce over the chicken and serve warm.