What's best way to improve handling

[Don]

Cursing the interstate in the 35 (I-64) the other day with new radials and Columbia, 60 was no problem,nice and smooth,till hit some bad pavement,before I knew it the car was wanting to change lanes with out any help from me,slowed down till I had more control ,,what the heck causes this,put a torsion bar on last summer ,helped some on curves, not sure about my shocks,would improved shocks help this or go to tube ,I like to drive my car and will probally never be in a points judging,,,,,, .any ideas ..do have the later model steering gear,big improvement..everything is tight.