Just FYI, I replaced the rear u-joint and it completely solved my vibration issue.

:jump:

Well that was easy :tu:

Thanks guys for the heads up. I am starting to think U-Joints as well but I would think the vibration to be more constant if it were them. The vibration is getting more common now and had the guy that put in the clutch drive it which he said it could possibly be the tranny. I don't think he is right because, I can disengage the clutch, have the truck out of gear, and coast down the highway and still hear and feel the vibration. I'm still troubleshooting though cause I cant figure out where the noise is coming from so any other feedback would be very grateful....

Seizing joints are intermittent...until they completely seize.

Thanks Steve, I just called and found out that 15.99 for a U-Joint isn't bad. So, I think I might just replace them and see if that works. It sure beats the tranny work that the garage that put the clutch in is wanting to do just to find if the noise is coming from the tranny.

Before buying joints, pull the shaft and inspect it...

Sorry so late getting back to the thread. I wanted everyone to know that the rear u-joint was toast. No pivoting whatsoever and when we got the cap off, we found rusty dust. I replaced both u-joints located on the drive shaft (the use of a ball or u-joint press is highly recommended). Problem solved! Hopefully this thread may help out some other cummins driver having the same problems.

Similar problem
 

Before you changed out your rear axle u-joints did your truck make a rhythmic "growling" sound? Mine also has a real small amount of vibration in the stearing wheel and seat and interior componants. So far I have replaced upper and lowe ball joints, both front hubs. Axle u-joints in front. Pulled axles from rear and removed hubs to checks bearings. New brakes/rotors front and back. And the problem persists. I only checked the driveshaft u joints for tightness and lack of play. Did your truck show some similar problems prior to fixing it or any other ideas?

What year of truck...if its an early 3rd gen, it might be the 70mph vibrations.

2004.5
 

Its the 2004.5. Bought it new and this problem just started last week.