Brake pedal vibration only when braking at high speeds

I am now leaning towards the back brakes and have new drums coming under warranty just in case they are out of round. I also have some speculation since the hardware on the front was just enough off that I needed to buy the OEM clip that something might be off with that. Serves me right for not inspecting the originals to the replacement parts close enough. Lesson learned on that but now still trying to diagnose…