Growling vibration only in 4x4/ 4h

I have a growling vibration that can be heard and felt on the floor boards of the truck going between 110-120 km/hr, and sometimes at 80-100 km/hr while in 4h. I had the ecgs bushing installed before because I had the same vibration before but only in 2h, not in 4h. Since the bushing was installed there has been no issues in 2h. Now just in 4h. Anyone know what could be the issue here?

I'm running a revtek 3 inch lift level with 285 wheels -12 offset if that helps at all.

 

Are you driving on dry pavement in 4h at that speed? If so, there is your problem. You are causing some binding and you can hear it in the driveline.

 

Nope. It's ice covered.

 

Hmm, then something along the line is now out of balance or grinding. Did you remember to refill the front differential with gear oil after changing out the bushing?

With it being speed dependent that would almost suggest one of the shafts is out of balance and since it's only in 4WD that would eliminate the front two CV shafts since they spin even when the truck is in 2WD... which leaves the front driveshaft or differential. I know that might not help but your issue is probably there.

 

The dealership installed the bushing. So I have no idea if they topped it back up. I would hope they did. I will bring this to there attention when I take it in. Thx.

 

Having the axle under load at that speed could be bringing out early symptoms of a wheel bearing going bad.