now the road condition is quiet better, so i think their is no need to engage 4x4. But still if u stuck at some point or the Prado is crawling slowly and u need some speed so put ur auto gear to N, then engage the 4x4 to the top position, i.e L4, if u move the 4x4 gear lever forward for 1 time it will engage H4, which is not helpfull on steep road, then when u move it forward for 1 more time it will come to Neutral, then moving it forward for third time will reach the correct gear i.e L4. In this gear , the prado will b 4 times more powerful and can climb almost any kind of track. Remember on L4 ur max speed should b 30 km. While disengaging the 4x4, u hav to put auto transmission to N, and bring the 4x4 to the lowest level i.e H2. While engaging 4x4 u will find a light on speedometer, on disengaging it will go away.
Best of luck for the trip. Do share ur experiences with pics