It happens. I always love to share my big nasty DW story.
Mine had death wobble stock & brand new.
Didn't surface for about a month after buying it. But it was pretty bad. So bad it caused me to keep losing wheel u-joint caps. I must have followed every piece of advice out there on solving death wobble trying to fix it.
Finally found the problem...
YouTube - Death Wobble
Lower ball joint, loose from the factory. Stupid dealership (Frank Fletcher Dodge of North Little Rock Arkansas - notoriously terrible service dept) didn't find it after being in the shop with it 3 times. They kept telling me to replace the steering stabilizer (again, I'd replaced it 3 times, including 2 aftermarket ones), but that they wouldn't do it under warranty due to my aftermarket tires
Note... the tires I had at the time were some MTR/Ks the same size as stock ones. They also suggested getting an alignment (no help, did it twice), and one tech there suggested longer front sway bar links.... ???
So I eventually ended up finding it. Showed the dealership the video. Showed them the balljoint and how you could see light between the crown nut and the axle C. Showed the the stock pin still through the crown nut, never moved. Told them I wanted all 4 ball joints replaced.
Dealership didn't fix it. They kept my jeep for 3 days (also wanted my throwout bearing replaced - they didn't do that either).
First, they claimed that they tightened the crown nut and put lock tite on the threads. Only I'd already checked it and the crown nut hadn't moved, still had mud on the threads. Told the tech I wanted to speak to the service manager. So he came and said it wasn't actually loose, said they tested it with a pry bar - so they didn't need to tighten it. In fury, I stormed off saying I'll fix it myself.
So I rented a ball joint pressing tool from the auto parts store, pressed it in the rest of the way (it was way way loose) and tightened the crown nut up. Fixed.
But what fun dealerships can be.
Later on, I got DW again. Bent tie rod. That was an easier find and easily fixed - replaced with a solid one.