I have a similar vibration at the same type of speeds and specifically under load. It just now became noticeable since I put the front radius arm poly bushings in. *I put in the rear and drove it for a week and then did the front. I guess that would isolate my vibration to the axle since poly bushings are stiffer and would transfer the vibration better than the worn out rubber. When I changed the front diff oul it had metal in it, only about a quart came out and I got 1.5qts back in. I also have the Ironman 2in lift.

Could it be worn bearings in the diff causing the pinion angle to change? This would explain why removing the driveshaft makes the noise go away..?

 

I did the ball joints recently and the fluid in the diff seemed fine. And I figure that it's got to be something that is under some kind of load given that it happens when going from 30 up under a slight load. I'm gonna try the front output bearing.

 

I just got a call from the driveshaft shop. I dropped the front shaft off just to get it checked in case. They told me the new tom woods shaft is slightly bent and was unbalanced according to them. I'll pick it up tomorrow and see if that solves everything.

 

Pretty sure that will solve all your issues.

 

So the driveshaft which was new from tom woods and the second one from them was bent. This hasn't fixed 100% of the vibrations but it is far better than it was. I'm going to do the transfer case output bearing this week to try and solve the last of it.

 

I had the same vibration you described, removed the front drive shaft and found the t-case output flange to wobble a little. Concerned it would need a bearing replacement I went to loosen the nut holding the flange and to my stunning surprise, it was loose enough to remove with my fingers. Tightened the nut up to torque spec, reinstalled the drive shaft, no vibration on acceleration, deceleration, or coasting. Couldn't believe it.