I have a pretty rapid vibration at and speed above 30 but throttle has to be 1/4 down and thats it wether im letting off or gasing it. I have a 30 foot chain in the bed of my truck and i dont feel the vibration inside the truck very much but that chain is just vibrating like crazy in the bed of my truck witch tells me that somewhere in the rear of truck is just vibrating like crazy and it only does it at 1/4 throttle HMMMM

 

i get this too...i'm interested as well.

 

Mine was kinda like this when the U-joints were about to crap out. It'll get worse.

 

I have a similar issue. I bought a new rubber exhaust hanger support but I havn't gotten a chance to try it out yet. It'll be a while before my rig is running again but if your support seems worn out you may want to try this. They are only like $10-15 from the dealership.