vibrations

Can anyone tell where these vibrations are coming from?

Here is what I can tell you:
1999 XJ 4-door
4.0L I6
AW4
3" Skyjacker doubleflex (installed 2 years)
JB Conversion 231HD (installed 1 1/2 years)
Tom woods CV drive shafts front and rear (installed 1 1/2 years)
Superior Dana 30 w/ ARB front (installed 1 1/2 years)
Superior Dana 35 w/ ARB rear (installed 1 1/2 years)
31x1050R15 BFG MT's

SYMPTOMS:
-A strong vibration developes around 55mph+, the same vibration is more prominent in 4wd
-When slowing down to a stop at about 2-3mph you can feel and hear stuf that is like a loose spinning part
-Jeep dealership said all (front and rear) U-joints are fine
-Axle kits installed by a Jeep dealership
-When I shake the yoke at both differentials there is no loose feeling
-The vibration is feels like it is coming from under the front drivers seat which indicates something along the front drivetrain



Based on what I have seen I think there is something wrong between my 231 and front axle. I used to think it was the U-joints, but just a few days ago the dealership said they were fine. I don't think it is the pinion bearings due to the yoke not being loose on the D30. I find it hard to believe that my JB Conversions 231HD has a bad bearing in it after only being installed for 1 1/2 years roughly. Any help is appreciated.

Thank You

One method of determining if it is in fact the front driveshaft would be to simply take it off. Remove the d-shaft and then go drive it around. If the vibration persists then you know its NOT the front shaft. If the vibration is non-existent then you know that something along the front d-shaft is causing problems..

-jm

I will try that, thank you.