Land Cruiser 200 Suspension Upgrade

We have same size van and are pulling with new cruiser with stock standard suspension, for the moment it's fine but we suspect that it will need upgrading when they are a bit more warn in.
We put it in low range on the weekend and found that it's not as simple as "putting it in low range" we had alarms going off and decided we need to read book and practice on contour bank, would guess we need to push other buttons not yet discovered

Thanks, that works, no alarms going off now
We were on a private road on a farm and from a standing still start had to pull the van up a righthand bend and up extremely steep pull on "marbley road" We had enough power, the wheels were slipping and you could feel the technology kicking in to adjust the power to the wheels. There was a tractor on stand-by and plenty of on lookers "You won't make that"
We did!!! but I was holding my breath

We traveled from Gunnedah to Port MacQuarie packed over Xmas NO VAN and only got 7.8lts/100ks. The car had about 2000ks on the clock.
Its now got 5000ks and we will going from Gunnedah to BT up New England Hwy at the end of next week with van on, so that will be a good test, We have traveled a few back roads around here and it does seem heavy on fuel but we are only guessing.(it sure does pull it fantastically)
Will give more details in a few weeks