like what initialD said..you might have too little droop at the rear causing the weight to be transferred all to the front leaving the rear end floating and causing oversteering when throtle is released...try putting more droop at the rear or put stiffer springs at the front...if it still over steers try changing oil to a hevier weight to slow down weight transfer or arm travel...
everything is all about weight transfer from side to side, front to back corner to corner of the car...
one more thing, check for tweak...see xxx-s tweaking...