In medium bowl, combine 3/4 of the bottle of buffalo wing sauce and ranch seasoning. Stir to combine.
Place chicken breasts in slow cooker and pour wing sauce/ranch seasoning mixture over chicken.
Cook on low for 6-8 hours.
Shred chicken breasts, add butter and additional wing sauce and stir well to combine.
Cover and cook on low another 30 minutes.
When chicken is almost ready, pre-heat broiler.
Place slices of cheese on bun tops and melt cheese under broiler, about 1 minute.
Serve buffalo chicken on buns, with lettuce and topped with blue cheese dressing.