In a large bowl, stir together the sour cream, cream of mushroom soup, cheese, onion, salt and pepper. Gradually mix in the hash browns until evenly coated.
Coat the inside of a slow cooker with cooking spray or butter. Spoon the hashbrown mixture into the slow cooker. Cover, and cook on High for 1 1/2 hours, then reduce heat to Low, and cook for an additional 2 1/2 hours.