Synthetic Dexron ATF is always the better choice.
I would recommend every 30k for regualr dino ATF and if you go synthetic, double the interval to 60k. I would be willing to bet it has never been done on yours, but you didn't state how many miles you have on it. In most cases, this service has a tendency to be overlooked.
Check out the other sites like NPORA
Nissan Pathfinder Off-Road Association (Powered by Invision Power Board)
There are links there to help you download manuals. Use the search!!