Join Date: Apr 2003
Location: Western Massachusetts
I had this very same problem - and thought it was exactly the same thing. However, I just installed a RE 3.5" SuperRide kit and the SLAM is gone. I didn't touch the gears... only changed shock, leafs, and removed the sway bar. One of those three things was making this noise - perhaps causing "axle wrap" or other loosness? I was surprised that the noise was gone, but something was definitely loose back there.
I know this isn't much help, but maybe it gives you other things to check (bar pins, loose sway bar, weak springs?, etc.) I see you are to install some leaf packs... check your shocks and when you throw the sway bar in the trash, noise might be gone.
'93 XJ, 4.0L / 5-speed, 3.5" RE Super-ride on 31s