In a large bowl, combine buttermilk, pickle juice, 1/2 teaspoon garlic powder and cayenne pepper. Add chicken and fully submerge. Cover with a lid or plastic wrap and refrigerate for at least 8 hours and up to overnight.
Add 1 1/2-inch of oil to a cast iron skillet. Heat over medium heat until 350 degrees. Meanwhile, bread the chicken.
In a pie plate or shallow bowl, combine flour, salt, pepper, 1 teaspoon garlic powder and pickle seasoning. Remove chicken from marinade and let excess drip off. Place in flour and coat well. Set aside. Continue with remaining chicken.
Once oil is hot, add chicken, making sure not to crowd the pan. Cook for five minutes per side. Remove to a paper towel lined plate. Slather buns with mayo, add chicken and pickles and enjoy.