[Bang from the rear end over bumps]

I've got the same issue with my 2000 td5, raised it 2" with HD springs and shocks to suit, also fitted double cranked trailing arms (as there were no single cranked available) with superpro poly bushes. It's almost as if the springs are under too much pressure and slam the axel down over bumps...I've been told most of it could be A frame joint bushes and movement. Yet to replace.

[diff lock not engaging]

I've got a similar issue although my lever works fine, yet no difflock light on the dash nor does it engage. I'll pull it apart tomorrow and check for blockages, unclipped wires & linkages and see what the heck is going on under there in the shadows..