Place the chicken breasts into a slow cooker, and pour in 3/4 of the wing sauce. Cover, and cook on Low for 6 to 7 hours.
Place coleslaw mix in a large bowl. In a small bowl, blend together the ranch dressing, mayo, sugar, and lemon juice. Add to the coleslaw and toss to coat.
Once the chicken has cooked, add the butter, and shred the meat finely with two forks. Pile the meat onto the Big Marty rolls, and splash with the remaining buffalo wing sauce. Top with coleslaw and serve.