Getting the Right Suspension

Hi ive just put in some knew Monaro 4x4 suspension in my van which isn't 4 wheel drive it now feels very squishy.
I have never had this problem with the original electric suspension my thoughts are maybe i need to get stiffer suspension
or new tighter trailing arms?
Ive heard from another post that Pedders sport suspension was good for there super custom but they're made by Monaro as well
love to here some feed back