You leave the O/D on unless you are towing and the transmissions repeatedly down-shifts, then up-shifts to keep up speed. All the shifting is tough on the transmission, so you wait until it down-shifts and turn off the O/D, which keeps it in the lower range. With the CRD, the engine has enough torque that this problem is almost non-existent unless you are towing a heavy trailer in mountains.
KJ is a Jeep designation for the Liberty. There is probably some sort of engineering logic to it, but it's just a way to designate the various bodytypes. All the designations are something-J; KJ, TJ, etc.
_________________
TxAshurst
'05 Liberty CRD
Mod.s to date: Added biodiesel and mud, but not in the same places; Upgraded tires to General AT2 M+S 235-70R16; U-Haul towing receiver; front tow hooks