[69Cobra]

I think you are excepting the suspension to separate without traction and that's not how it works. The tires have to hook to some degree for the rearend to want to rotate which is what makes the suspension separate. Think if your car was on ice and you dump the clutch. You are not going to get any separation because you have no traction. Put a set of 3056 M/T's which are the 9 x 29.5 stiff sidewall on 10" wheels and you will see a completely different car.

Also, even tho you have 12.5 tires you have them mounted on 8.5" wheels which is not helping you.

Don't forget about the front suspension. The front and rear have to work together.