death wobble

[3-lot]

jack up the truck under the lower control arms till front wheels are off the ground.
grab top/bottom of tire and shake in and out and see if theres excessive play somewhere, do the same thing side to side, that should tell you if theres something worn out in the front end (ball joints, bearing, idler/pitman, etc.)
if you feel something bad, get someone else to shake it for you so you can watch and locate the problem.
if nothings worn out, rotate tires front to back and see if it makes a difference.
-3-lot

 

[ravingmadman]

Hm. Could also be a U-Joint starting to fail, if all of the above check out. It isn't magic, there's something going on. You'll find it.

 

[yooformula]

I had similar issue shortly after replacing rotors and turned out the caliper bolts broke and while driving on the hwy the caliper came off. Luckily the rim kept the caliper from coming off from the car.