Probable a typical newbie question, but I have searched already and tried everything that I found. I have a 98 zj the I just upgraded to 6.5" Now I get d/w at 40 - 43 mph. I have adjustable upper and lower ca's, new shocks, new dual strearing stabelizer, new adjustable track bars (front and rear), new addco swaybar, extended drive shafts, and new tires.
after installing everything, had d/w so I took it down to a local shop (the offread shop in dallas) They had it for a week and were unable to correct it. They did a full "chassis alignment" to adjust all the arms and bars. No change. So they tell me "you did not install it correctly We will need to take everything off and reinstall it correctly" Well last time I checked there is only 1 way the parts fit. But I say "ok, your the expert it you think that will fix it go ahead" Well the installed it twice and still had not change. (At least they didn't charge me) But they did have my rig for 2 weeks...
So then I take it home and look everything again and again. Everything is torqued down the spec. Checked to make sure that nothing was bent, nothing is bent.
So then I take it to anouther shop (Dimond offroad also in the dallas area)
They do the same things over again, still no change.
Any Ideas???
I am about to put it back down to 4.5" again, if I can't get this fixed...

How is your steering geometry? Are you running stock steering? If you are, look into an aftermarket steering setup or swapping to WJ knuckles and steering componets. I had death wobble when I went form 6" to 8.5" on my xj, but after I adjusted the caster to spec and threw on a ZJ pitman arm (One inch more drop than a XJ) it went away.

Get your alignment print out.
What's your caster?