2008 Volvo shaking

When was the last time your air leveling valve was looked at? If it is not set correctly, it can cause all sorts of odd vibration behavior.

Any chance you have either a bent wheel, or one of the tires is not correctly mounted and off center?

 

I would definitely look into the suspension. Make sure no bushings are missing and then make sure the air ride pumps up properly. Sounds to me like you're getting a suspension wobble. Usually simple to fix

 

Look on driveshaft for missing weights, are you talking about steering wheel shake or floor of truck shaking?

 

I would look at the suspension then. And yes make sure the u joints and drive shafts look good as well.

 

Crawl under and see if there is any play in the driveshaft check both.

 

Check drive line possibly a bad ujoint. How ever I had a similar problem with a 2005 century. It turned out it was bad king pins, so check them as well. Good luck