Dumb question..... are the bolts through the new k member to the frame all good and tight, and no slop? As said 3 posts above, for it to do what you describe, means that the LCA is moving around relative to the chassis a LOT; that could occur at 3-4 places: k-member moving, LCA pivot moving, LCA inner bushings moving (torn apart), or strut rod loose.
If you have poly bushing in the LCA, then that one is least likely. If the LCA bushings are rubber, they could be shot if old, or, if new but you tightened the pivots while up in the air and front wheels at full droop, then they are probably torn all up.