I'm with Wallington, no need to change it, unless you're planning to repeatedly take it on the strip. If you so wish, for peace of mind, your gear oil can easily be changed and you can also buy an additive from GM that you can pour in to help with (what I presume in your case) your posi/limited slip diff. A long time ago I noticed a little bit of grinding when turning tight corners, and changing the gear oil and adding the additive took care of it.
Also, if you "were" planning on placing better gearing, make sure your transfer case supports the gears you're swapping over to. I may be wrong about this, but if you have 2:73 gears, it won't support a set of 3:23's or 3:55's and above. Maybe someone can confirm this with me. In any case, if it's more highway driving that you'll be doing, 2:73's - 3:08's are fine.