Just to clarify, the car isn't permanent 4wd, it doesn't have a centre diff as per land rovers.
It is primarily running 2wd, but has a active torque on demand transfer box, when rear wheel slippage is detected the transfer box clutches are engaged to allow drive to the front, up to 50/50 split.
Engaging low ratio locks it into 4wd, with low ratio gears, hence the speed limitation, I'd recommend having it in neutral and hovering the brake pedal when doing a range change, allows the drivetrain to turn to get gears aligned, much kinder on the transmission.