My steering wheel violently shakes, then settles down. It doesn't matter what surface I'm on-it shakes even on smooth surfaces.

This is what has been done so far:

Replaced: front shocks, front tires, sway bar links, idler arm, pressure control valve and rotors.

Checked ball joints, rag joint, tie rod ends, pitman arm and brake pressure at calipers.

Front end alignment

Adjusted steering box

Cleaned sliders

Any suggestions for what to do next?
Thank you

First question is, on the ground is there any free play in the steering visible when moving the st wheel off center and noting the subsequent movement of the wheels? Was any work done or did anything happen just prior to this condition occurring? Pressure control valve for the steering? If so watch for air in the system.