Ok, Got it fixed,
It was a bad diff angle like you suspected.
Runs great now, the new springs are a huge improvement over the stock springs.
Nothing can fix the short wheel base low weight problems with ride quality, but my tires can ride up and over large bumps now without ramming the whole body upwards.
Ride is still stiff but more comtrollable, much greater articulation than stock of course.
Thanks for all your help
chris