Catching back up.
First , Mr. Blaine trumps anything I say , I'm observant , think conceptually and have some experience .
He has vast experience , and smarts to go with them , and understands steering geometry at a level I have never seen before. Always read his posts .
Back to your front end .
You have eliminated a lot of variables in your approach already.
If you have a dropped track bar mount (you do) and a dropped pitman arm (you do) they negate each other so you don't "have" to start over . It's not the preferred set up , but my 03 has it with a Rough Country lift with a dropped track bar mount and dropped pitman arm and it drives car-like...what you end up with is both the track bar and drag link at a more horizontal angle , and that is considered to be good.
WHAT YOU NEVER WANT IS A DROPPED PITMAN AND STOCK TRACK BAR MOUNT . I just removed this from my 06 Tj, and it is a must for good handling . Dropped pitman arms are largely out here due to a one size fits all mentality by lift manufacturers.
Again , a dropped arm and track bar is not the ideal set up for under 4" of lift , but it doesn't cause or allow death wobble more than a normal set up to my understanding.
Death wobble isn't a set up problem generally as much as a movement problem , so something has crept up on your rig that has begun to allow movement that isn't obvious when dry testing or on the rack . Note that statement.. something has crept up. A fractured weld , an elongated hole, an undertorqued bolt on the track bar (after market track bars often have near double the torque spec). What stands out is you didn't change anything , it just randomly started , which tells me something changed itself for you .
What you do need to watch for is excess movement by the dropped track bar mount first . I have looked at your picture until I am straining but can't make out the frame side mount . What I think I see appears stock ...note the word "think."
What does seem to grab my eye is there seems no exposed threads below the pitman arm, my rough country pitman arm has 4-5 threads below it. Maybe it's camera angle .
There is no such thing as "unfixable death wobble" to my knowledge , unless something is basically scrap yard condition ...and you have a very nice looking , clean TJ ..I really think this is going to be a matter of finding something loose that really surprised you .
I hope you can post a pic of the mounts on either end , and check with the exact track bar you have now manufacturer on the torque specs .
Don't be casual .
Also , another brand track bar could work in your mount , but it could also be a big part of the issue if it isn't compatible in design .
I also suspect your death wobble is less tires and more on the track bar and /or linkage simply by the tire size and condition, as well as the fact it takes higher speed and a bump to get it going .
Knowing the steering is new , it is really likely something is either happening at the track bar , the frame mount or the pitman arm .
I would not buy a single part , but focus entirely on diagnosis , and unless something is way loose , I would not worry as much about the control arms as I would anything designed to allow or control left to right movement , which is steering linkage and track bar respectively.
Keep us posted.