A couple places I have posted too.

http://www.cumminsforum.com/forum/3r...-1500rpms.html

and

http://www.cumminsforum.com/forum/03...ing-worse.html

These two might get you some answers you are looking for. Read them both. I have given up. Last trip to a different dealership has amounted to nothing. Corporate recognizes the issue but can't or won't sink any more money into the research anymore. I don't think they have put forth any effort at all to look for a cure. I would call corporate and tell them you are having the drone issue and document it. They will give you a number if you are still under warranty. I'm out now, but they have agreed to fix anything that "they" think may be caused from the vibration.

The last thing I have tried was to install a 5" Diamond Eye exhaust and an AFE stage 2 intake. it drones out the drone now

 

Maybe try swapping the rear driveshaft. I had a vibration on my 04 start suddenly. dealership told me there was cardboard glued inside the driveshaft to reduce humming and it had broke loose making the driveshaft out of balance. I still have a hard time believing there's cardboard in there, but the vibration went away.