Well guys I had my two piece driveshaft installed about a year ago on my 08 Sierra CC, but recently I lowered the truck about another inch out back and it drove just fine for a few weeks but now it vibrates (the whole dash board shakes) at 65-75 MPH only and after or below those speeds it goes away and drives fine.....any idea what it could be possibly be? Maybe the angle of the drive-shaft?...I checked the U-Joints and they look good so I dn't think those are it.

 

Sounds like your pinion angle is wrong to me.

 

^^^^ i was gonna say the same thing. My truck has been doin the same thing. Pretty sure its the pinion angle, got to fix mine to.

 

It is likely that it is the pinion angle. It could also be that the operating angle on one of the joints is too narrow. Do you know what those angles are?

 

I'm not sure what the angles are...I noticed it vibrates a lil more now...........any idea how hard it is to fix the pinion?