Odd Vibration / Rocking

[baseballguy]

I am fairly new to trucks let alone Powerstrokes. I have had my fair share of sports cars ranging from 300ZX's to a Camaro SS.

I issue is this...

The truck seems to me, very violently bumpy on freeways. Almost to the point where I cannot read the dashboard. It doesnt go left and right, its like a rocking motion. Front and back. A friend of mine suggested to put about a thousand pounds in the bed of the truck to see if it helps smooth it out. Im not sure what else to do?

I know that it is a lifted truck and is going to be not as smooth as stock... but I had a slammed 01 Camaro SS before this and it was a heck of a lot smoother than this.

I bought the truck with the lift on it already, and I dont know how long it was on it to begin with. Would a new set of shocks help?

I have had the violent "Death Wobble" before. To the point where I had to pull over. This happened when I first got the truck and I hadnt done any research to what it was. I understand that a Steering Stabilizer would help a little. But thats not my problem here.

Please, any input would be greatly appreciated.