I'm having pretty much the same problem. New in July, wheel bearings, Powerstop pads and rotors and new shoes w/hardware in the back. Any braking above 20mph it shutters like horribly warped rotors. It's only been doing it the last few months and mostly a pavement Prince lately.Nice. That's what I'm leaning towards. I need new brakes as I'm getting a violent shutter at anything over 30 mph and trying to stop. So figure why not just convert now.