What causes the car to understeer and oversteer

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.

It’s a pretty common place for the welds to fail. The factory welds weren’t always great, some K’s were a lot better/worse than others.

I seam weld and reinforce all of my K frames. The steering box mount and LCA pivot mounts get gusseted, I add a skid plate, etc, similar to what Firm Feel does for their K frame reinforcement package.