Mine was NAT 3 until last month and it changed to NAT 2. I have absolutely no idea what I did to change it, but I have been unplugging my hub a lot recently so try that.
It has also been said that you can restart your PS3 until it changes to NAT 2, but the number of restarts is different for everyone and is not guaranteed to work. The reason being is the PS3 uses different ports every time it connects.