What causes the car to understeer and oversteer

Well it may just not be tightened down. The torque spec is pretty high for those bolts. I forget exactly what it is off the top of my head, but if it wasn’t torqued properly the bolts can loosen up.

The steering box mount may also be damaged. That’s what happened on my Duster. The welds holding the steering box mount to the K-frame cracked, and the whole mount would flex back and forth when I turned the wheels. If that’s the case the K-frame will have to be pulled out and welded.
that's how I fixed mine. I had Dan H. in Milton reweld the mount on the K-frame. I believe I had him add a gusset or two while he was at it, also.