Hi Jared, Are the rear springs the standard coupe springs apart from the eyes being reversed? or have you added leaves?
Are the kumo`s convetional or radial slicks? (Radials need to run alot more camber than 2 degs. more like 4.5.)

What tire pressure are you running?

What brand/valveing on rear dampers?

Does the diff have any lateral locating device?

Does the rear end have suficient travell? (you need min 3"droop and 4" bump with a live axel, thats 7" overall)

I`d try adding at least 2 degrees more camber and a little more toe out (about 4mm total) at the front.

The rear could be caused by insuficient droop travel on suspension/dampers, serverly under inflated rear tires (if the condition exists only with steering input) or exesive rebound on rear dampers.

Simon.