Dana 60 kingpin death wobble

[1972RedNeck]

Had a '93 Dodge that I got from my late great uncle that I ran for a couple years until the body fell off. When I got it, it had a minor death wobble. I rebuilt the king pins and u-joints and all was well for awhile and then a hint of death wobble came back. Added a flat washer on top of each king pin spring and all was well for about 40K miles until I parted it out.

Then I swapped it under my '72 K20. From the first drive, I had a terrible death wobble around 40 MPH. Drives great at 50+.

I got another new set of kingpin bushings and springs (genuine Spicer) and swapped in. Kept the flat washers on top of the springs. Fixed my death wobble for about two months and then it started to come back ever so slightly. Added a steering stabilizer shock which fixed it for another month or so and then a hint of death wobble showed back up. Fast forward two months to now and it has a terrible death wobble.

I assume that new springs have enough tension to keep everything tight and as time goes on and they compress the death wobble comes back?

How many washers can I add before the the spring bottoms out?

What is causing the death wobble and is there anything else I can do to fix it?

Skinny tires (8R19.5) at 80 PSI. New spring bushings. TRE are near new and tight. Tires wear perfect. Truck drives absolutely perfect, other than the death wobble.

Heavier tie rod and hydraulic assist steering? (Kidding - for the most part...)