I had this same problem. I had 4 cyl. springs and yes they do ride a lot nicer than others and give the car some weight transfer abilities, and sits about a 1in. lower than stock. But the springs are not your problem. Its the geometery of the rearend itself, meaning lower control arm geometery.
What I did that solved the problem is put chassis engineering lower control arms on, which are identical to the SSM and a little bit cheaper, and problem solved. It changes the center of gravity under a launch/load condition and thats why it fixes it. Hope this get you in the right direction.
