Extreme Oversteer

[ubtripn]

HI all, I need the boards wisdom on this one, I have replaced almost everything on my 68, the front end has been rebuilt and I added a saw bar and power steering. Now I know modern power steering adds more pressure or something to the steering wheel at higher speeds and the tires turn less as you turn the wheel. I think its called variable speed, anyway I installed power steering along with a new steering box but at 65 I can twitch and change lanes. Any thoughts on how to change this. I have about one and a half turns from center to lock. The truck can be a bit scary to drive.