WTF is the shaking @ 75+ mph?

Tires increase in diameter as tire RPMs increase (think funnycars). If the belts are not uniform (as in excessive belt overlaps in some parts of the circumference), that part of the tire will not expand as much as the other parts of the tire; causing an out of round condition. This shows up more and more at higher speeds.

 

I had a 2008 that never did this. My 2015 does this...sounds like there isn't much concern..I rarely go on the freeway at those speeds so I am just now noticing this. It looks like my passenger seat will wobble off it's mounts. This occurs 75mph+

 

It is worth checking the tires for belt problems. Road force balancing should be sufficient.

 

FWIW, I installed the AP carrier bearing drop and the vibe is pretty much gone at speeds 75+

 

Is your vehicle lifted?

 

Did that help? I should do that too then

 

Is your truck lifted? If not, have you tried road force balancing your tires? Btw: what kind of tires do you have?

 

I do have a lift. It def has to do with the angle of the driveline and wth am I doing in a 3rd gen post? google took me here I am sorry

 

Good idea to correct the driveline angles after a lift. I am glad you got it worked out.