I have a 06 ccsb f350 4x4 with a 4.5 donahoe lift with stock wheels and tires. On the freeway I have a vibration in the seat and when you go over bumps it seems to vibrate more and shudder thats the best way i can explain it. all the way from 40 mph and up. I started with balancing the tires didn't change a thing. then rear pinion bearings (cause the seal was leaking) didn't change a thing. then the center carrier bearing nothing changed. then the three u joints nothing changed then had the drive shaft balanced still nothing changed. Anybody having this problem? Any Ideas?