Slow Cooker S’mores Chocolate Cake

Recipe: 1 box Chocolate Cake Mix, prepared according to package instructions 2 cups graham cracker crumbs 1/4 cup melted butter 1/2 cup granulated sugar 8 oz chocolate squares, such as Ghirardelli 2 cups mini semi-sweet chocolate chips, divided 2 cups mini marshmallows, more or less to taste 1 cup graham crackers, cut in large pieces….