on road runner have you fixed your truck yet?
did your lift kit come with a new adjustable pan hard bar or just the drop bracket?

 

I'm also having this problem on my 2000 tacoma. it will jump off little bumps in the road and sometimes feel like the back tires are jumping off to the side and landing on the road hard. i just got brand new tires on the back and the problem remained the same. im thinking it has something to do with worn bushings but I don't know what ones or where, Can anyone give some more thoughts on it?