Check the disc runout with a dial indicator while it is still mounted on the bike.

 

That's the first thing I would do. Plus, in a real fast stop, the back brake is not going to do that much because more of the weight shifts to the front. It's probably a coincidence.

 

Depending how hard the stop was, the rotor could have pulled the bolts out a bit. Maybe not enough to see by eye but enough to cause problems.

 

Put it in neutral, pump the rear brake pedal, jack it up and spin the back wheel. If you hear "whish whish whish" sound and it's dragging and then spinning easy while going around you cooked your rotor.

 

Well...ONE very, very hard brake.. Somehow wrapped rotor. New rotor, new pads, and so far issue solved. Thank you all for your input.