At above 65 mph my truck starts vibrating like mad doesnt feel like its comming through the steering wheel. Feels more like its in the floorboards. it has 105,000 miles on it any ideas what could be causing this >?

 

Sound's like a u-joint. Read the like below on how to check. But even then, you can still have a bad one. I had the joint replaced at a shop. All was good for 100 mile's, then I developed a 70mph vibration that I never had. I just installed a whole new driveshaft today, and all is well. The point is, I think the shop messed up some how, or something went wrong somewhere.

https://www.dieseltruckresource.com/...d.php?t=191055

 

Also the drivelines have small weights to balance them, Ive seen were those weights fall off causing vibration that isnt noticable ant low speeds

 

Yup U joints, I cracked and ground down the one right behind the transfer yoke to the rear end. It was a vib for a while thought it was a bad tire, then Clunk clunk VIBBBBBBB one day under hard accelration, knew what it was then