Preheat oven to 350°F. Butter and flour a 9x13 cake pan and set aside.
Prepare cake mix according to directions. Spread batter evenly in prepared pan and bake for 20-30 minutes until cake springs back when lightly touched in the center. Using the handle of a wooden spoon, poke holes across the surface of the cake, 1 inch apart.
In a large bowl, combine pudding mix and powdered sugar. Whisk in cold milk for about 2 minutes, until thick but pourable. Spread pudding over the surface of the cake, gently pushing into the holes. Cover the cake and refrigerate for at least a few hours.
Combine graham cracker crumbs, sugar, and melted butter in a small bowl. Frost cake with whipped topping, then sprinkle with graham cracker crumbs. Serve.