Yes, (in 4x4 applications the gear ratio/s match the front axle). 2 wd there is no front ratio to match.
replace the rear shock asorbers
Yes if it is the same length & after refitting the end of the jeep drive shaft to bolt up to the ford rear end
It is in the center of the rear of the axle.
No. The axles & suspension are completely different.
Not exactly, yj's were a spring under desiegn while the xj's were spring over. Width wise, the xj rear will work, but you'll either have change the spring perches on the axle, or change your center pin in your springs.
I'd look at the pinion bearing first. It's near the end of the rear end.
I believe that is the Dana 35
You can change at least half of the fluid in the rear end at Tuffys.
get a posi traction rear end and swap it out.
Dana 35 or Dana 44
The 2003 Jeep Liberty typically requires around 2-3 quarts of rear end fluid for a complete change. However, it's best to consult your owner's manual or a professional mechanic for the specific amount needed for your vehicle.
Yes, there are locking rear ends available from many after market sources.