The reason why both wheels are turning in mud is because the ABS is working.
there are 550 models that have an LSD switch, my 550 does not have the LSD and I believe all models have a VDC ( Vehicle Dynamic Control )switch, which is the same as the ABS in other vehicles. In Navara's close to $70,000 have the LSD, mine was only $65K and it doesn't have it, Bummer!
Hopefully that helps you Steve.