Beat 1/2 cup flour, buttermilk, grill seasoning, and egg together in a large bowl until smooth. Add steak strips; toss until well coated. Cover bowl with plastic wrap and marinate in the refrigerator, at least 2 hours.

Sift remaining 2 1/2 cups flour, garlic powder, salt, and black pepper into a large bowl. Remove steak strips from buttermilk marinade and allow excess to drip off. Discard remaining marinade. Dredge steak strips in seasoned flour; place on a baking sheet. Freeze until firm, 1 hour to overnight.

Heat oil in a deep fryer or cast-iron skillet to 370 degrees F (185 degrees C).

Lower frozen steak strips carefully into the hot oil, a few pieces at a time. Fry until golden brown on the outside, about 5 minutes. Transfer to a paper towel-lined plate to drain. Repeat with remaining steak strips. Do not overcrowd the fryer or skillet, and do not allow the steak strips to thaw before frying.