When I'm towing my 33' fifth wheel (10,000lbs) I get a strong vibration when I really get on the throttle (merging on the freeway kind of thing).

Light acceleration (up to 2400-2500 RPMs) is nice and smooth.

Any ideas?

 

is the truck sagging at all from the pin weight? you driveline angles when the rear of the truck is down is different than level. angles being out of line wil cause a vibe if the ujoints are starting to go, or if the carrier bearing is going.

what year, model, bed length, and cab type?

 

It's hard to answer this without knowing what you are driving. Take a minute it fill-in your signature. 2-WD vs 4-WD? Sounds like a U-joint to me. These Dodges are known to shudder some under a hard pull. Mine did this from day-one.

 

Sorry about the lack of info.

Its an '07 QC,LB,4x4 with the 5.9 and G56.

I'm right at 6000 miles.

The overloads are slightly on the rubber stops when the fifth wheel is hooked up.

 

sagging is causing the driveline angle to make a ujoint shudder.
there are 3 ujoints and 1 carrier bearing on the rear shaft of your truck.

 

Is it a vibration or a drone?

 

Definate vibration.

 

So other than airbags,nothing else I can do?

 

try shimming the carrier bearing down an 1/8" at a time till its gone.
or bags

 

You can see the size trailer I pull in my signature. There is over 1200 lbs of tongue weight on the stock Class IV hitch. It made the rear of the truck settle pretty good. Even though I could bring the ride height back with 1400 lbs bars on my weight-distributing hitch, uneven roads would sag the rear-end of the truck and the shudder was very pronounced. I installed a set of air bags, carry about 50# in each bag, and the problem has gone away. There are other threads on this forum that discuss this problem to great lengths. Do a search and read all about it!

 

Your pinion angle is changing. Best thing to do is install ladder bars. If done properly will keep pinion always at proper angle. I had similar problem with a 2005 6.0psd Excursion. Best mod I did with possible execption of edge with attidue and a seperate turbo timer.