Bumpsteer is nothing compared to this.

 

The DPA could be part of it but as stated check the track bar.

 

Do you have an adjustable track bar? Mine did this after adding an aditional 1" spacer. The front axle may need to be re-centered.

 

like i said sounds like Death wobble lol number 1 cause is trackbar triple even quad check it, and with the spacers you may need to recenter...

 

The mods are probably the root cause but I'd still check on the steering damper because the stock one even if not already damaged (see T.S.B.s) is surely not set up for the accentuated dynamics that are already in force due to them.
This is definately now a different vehicle than what the damper was spec'd for!
Sounds like it might be time for a double damper set-up.
Darn sight cheaper than a write-off let alone the possibility of personal injuries.
I had death wobble in a stock YJ once and didn't know up to that point in time that the exposed rod was pitted due to "stone blasting" and leaking.
The situation you are describing sounds more like too small a part that can't compensate for all the expansions in sizes of the rest of the suspension and wheel weights/forces.