Is this vibration the drive line?

Did you do anything or have anything done to the truck just prior to the vibration showing up?

 

Yeah, you need to get that looked at ASAP.

 

You dont by chance drive a mid 60s GMC crackerbox with a 238 in it do you?

Just curious because of your statement

 

U Joints.

Start there. If they be loose, bolts rusty and showing shiny or other things (Never grreased etc)

start working your way into the rears from there.

It's beyond me to squeak about anything more mechanically. A long time ago I usually made sure my U joints were tight on that shaft in the car before a top end run. The minute it gets onery and starts to viberate, it's not long before something (Or a few somethings) really fail. That's not what you want at 130 mph. One failed U joint drops the shaft which digs into the pavement and flips you end over end 20 times to your death. Imagine what it can do to a big truck cab that's plastic with a 40 ton weight shoving on it downhill.

Nightmares aside start checking small simple obviously seen stuff and work deeper until you find it. It might be simple it might be grotesquely expensive and cause you to question doing the fix at all. (Junk the truck and get a new one...)

 

No, not at all. But to me, it's a waste of time and resources to chase down a vibration whose source is not immediately obvious. Drive it until the source is detectable without any guesswork.