Originally Posted by DAVE67FD

You have a 2 piece shaft.

Many SD's inherently have this problem. My 06 never really had it until i switched tires.
Remember there is a difference between a vibration and a bounce and can be the result of many different issues.
If you load the bed is it eliminated? Fixes my bounce everytime.

Many different scenarios have come about on the subject in the past and has been typically attributed to frame oscillations. These can vary with different hardware like shocks, tires, swaybars, trailer hitches and has been typically reported to be more excessive with the long beds. Not to be confused with the "Death Wobble" which is a front end oscillation. (don't really want to get into that one)

Haven't heard of any real fix for the issue as i don't think there is one.

Originally Posted by Irelands child

The first thing I'm going to do is the Hunter Road Force tire balance if someone locally has that tool. It got worse with the new tires. Then, if no real change, as you noted, a wholesale replacement of wear parts (shotgun approach) starting with u-joints, carrier bearing, rear axle bearings, sway bar links and/or rubbers, spring eye bushings, then a front end overhaul. While it isn't getting much worse, I just don't like the constant beating on my skinny butt.

One thing I did notice - when I have my 35' 5er hooked up, not much, if any bounce. Springs maybe need to be loaded to remove harmonics - but today, no load but the 200# hitch 3-4" behind the axle CL , very little bounce but it's also 95* - hmmmmm

(I wonder what kind of problems Chebbie /GMC have??? Dodge??)

Originally Posted by Metalhead2012

You find anything definitive? I just did the whole front end on my f250 and it's done nothing to eliminatethat 49mph bounce. Everything seems to point to rear end components, or the wheels/tires.