There is this stuff that you can get at NAPA called sea foam, I know that is sounds weird but it works great .
It droped my co on my blazer about 10 points.
In my wife's jeep it was the t-case.
I did a drop kit and it fix the shake. How big is the jeep?
Is it a full time 4x4? It may ned a slip kit and new driveline.