Ok so it started vibrating at around 45 mph and ends around 60 and balances out and i dont know where its coming from. Firat though was a tire out of balance so i swapped all 4 tire with the ones off my 83 and nothing changed.
It doesnt stop if i switch gears (thinking it may be rpm related)
It stops if i let my foot off the gas or get up over 60 mph.
Drive shaft and ujoints seem tight and there didnt seems to be any play in the carried bearing.
Drive shaft bent or out of balance?
Put it up on jack stands and run it through the gears. Have a buddy check underneath when the vibration is present.
I shouldn't need to say this... but, DO NOT GET UNDER THE TRUCK WHILE IT'S RUNNING LIKE THAT!!! Check from the side.
Sounds like a bad u joint to me. I second Sin on that idea. The best way to know for sure is to check it in real time. If it's a u joint though u can just lift the vehicle up on stands and just yank on the driveshaft. There's should be little to no movement if it moves u need u joints.
Another thing you could check for on the driveline is a balancing weight that the weld came loose on. You would see a silhouette of where it used to be and maybe even an old spot weld. If the driveline doesn't turn up anything you might check the balance weights on your wheels. My wifes car threw one of the weights and the front end started shuttering so bad I thought I had a warped brake rotor.
the carrier seems to have a handful of play in it. Ujoints are tight. how hard of a project is this? it looks like its just a nut on one of the shafts, drop it and replace.
just because u-joints are tight doesn't mean that they aren't bad, if they are dry and binding, that can also cause a vibration. Usually there is a squeak involved when this happens but not always.
no squeaking but with as loose as the carrier bearing was I'm fairly confident thats the problem. it will move a good 1/2 inch. So I guess my approach will be to replace that and take it from there.