Have a look here:http://www.amsoil.com/mygarage/vehiclelookup.aspx
Diff fluid to use depends on your engine and 4wd system. I've found that the Amsoil spec charts are very accurate.
You can tell if it's limited slip by using the following test:
1. Jack up vehicle by rear differential (front wheels chocked)
2. Put transmission in neutral
3. Turn one rear wheel forward. If the other turns backward, you have an open differential. If the other side turns forward, it's a limited slip.