Transfer case vibration on 2003 GMC Sierra 2500HD 6.0L

[Toasty_McSpud]

I would like to ask for some help on diagnosing a vibration on my truck.

Symptoms:

-In 2 hi, traveling from 0 - 40mph, no vibration is felt until I release the gas pedal. Then mild vibration is felt in the front end. If I apply gas to maintain 40mph, vibration disappears.

-speeding up to 60mph, vibration is felt all the time, and worsens when I release gas pedal and continues until truck slows to below 40mph

-traveling at 60mph, if I shift into neutral and release the gas pedal, vibration persists until speed drops to below 40mph.

-vibration is felt directly at the transfer gear selector lever

-in 4 hi, vibration is not felt at all regardless of speed or gas pedal application

-transfer case was replaced 2 years ago with a GMC 3500 transfer case.

-the vibration changes as the transmission gears down with no gas applied.

-the vibration is not felt in the steering wheel only in the floor.

-this vibration has only happened in the last month or so.

- when I drive in gear 3 no vibration is present

 

What's been done to try to diagnose this:

-tires balanced

-4 wheel alignment

-new CV axles

-new hub assemblies on front end

-front driveshaft removed fault persists

-all the weights are on the front and rear driveshafts

 

My truck is a commuter truck and rarely sees off road or rough terrain

 

I'm struggling in finding more ideas, and would really like some help in diagnosing the noise considering it's only happened in the last month.

 

If anyone needs additional information, feel free to ask any questions.

[Franksor]

Did you ever figure what the problem was?