Rear end spongy after 4 / 5 static drop

[Fantom]

I lowered my '71 LWB using 2" drop spindles & springs up front and 5" drop coils in the rear. I relocated the rear shocks and also installed the short shocks. The back is real bouncy, and when I drive down a rough road it almost feels like it's bouncing side to side as well.

I love the look, but hate the ride.

Has anyone else had this problem?
Will replacing the springs with bags stop this?


Thanks,
Kevin