Another question fer a buddy!
Anyhow, a buddy has an 04, 3500, 6 speed, Banks 6 gun. No codes. I just drove it and it has a vibration in it right when you take off in 2nd gear. And when you lug it in 3rd. This happens at low rpm's. At first I thought mabee the clutch is startin to go. But, I dont notice any slip. It has 81,000 miles on it. He uses it to pull most of the time.
Any ideas?

 

You might be getting a stiff U Joint.

 

Drive shaft angle's.
There is a TSB out for this, mine used to have it pretty bad.
There is one quick fix that will dramatically decrease the take off vibration:
I loosened up the carrier housing bolts (2) then pushed the carrier towards the passenger side about .75"-1" as much as they would allow in their respective holes.
That cleaned up MOST of the take off vibration.
The TSB calls for adding spacers to the carrier housing. Although that may be the proper fix, when I did my adjustment my 2 driveshafts are now in-line correctly and no longer have an angle between the two (much more true).

This quick fix did provide a night and day difference in driving comfort. My rear view mirror used to vibrate it was so bad, that is now gone.

Good luck.

 

Thanks a bunch man. Mucho appreciated.