Need to stiffen my rear 68 dart suspension

I have .960 torsion bars
Custom upper control arms
nylon bushings
Modified braced lower control arms
hodgkis front sway bar
Wilwood front and rear brakes
frame connectors
torque box connectors
6 point cage welded
front frame shock tower braces
brace tieing shock towers together
REAR
Hodgkis sway bar
stock new leafs
KYB shocks

The back end of my car slides out in the turns when I am PUSHING IT trying to keep up with the fast Nissans, porches, BMW's

Not to many people care about road racing MOPARS so help is hard to find!!!
Lots of old FAST Mustangs but they don't get to excited about the DART

I SO APPRIECIATE ALL YOUR INPUT GUY'S


sounds like a nice set up
could the problem be to much throttle in the turns causing wheel spin and resulting loss of traction?

what rear? locker? sure grip? open? with any limited slip type rear, power in a turn must be carefully balanced

I am sure "autoxcuda" will chime in with some good advice any time now