The manual that came with your car tells you the service grade of lubricant required for the rear end, the tail housing, and the manual transmission (if you have one and change it at the same time). If you are 4WD, you do not have the tail housing but need to think about the transfer case too. It seems like the tail housing and manual were GL-4 and the rear end is GL-5 but my memory could be off, please check.
I found it easiest just to order the lubricant on-line from JEGS. They list the same service information in their catalog so it is easy to get something that meets the requirements. I used synthetic because I thought it would be a little better and I think it was only $8/qt.
I think it is only the differential (rear end) and tail housing that I had to change to meet the service recommendation at 7K miles. I did the manual transmission too partially because the tail housing took so little and I did not see what I was going to do with a pint left over. It was also one of those "while I have it on the stands and am under here" situations. You need it level so you need to put it on stands at both ends which makes access to the transmission available and relatively convenient.
This involves more jacking of the vehicle but is not much worse than changing the engine oil (not that changing the oil is so simple on the GV with the 2.7l but it isn't really as difficult as I have made it at times either).