Not required to drive backwards for 7.5m, but one day it might help.

 

Well it still does not answer the question why I can only lock diff in 4 LO and not 4 HI

 

Someone mentionned in another thread that electronic rear diff only locks in 4lo. It does make sense for off-road driving.

 

The diffs are designed to only engage in low, and the front after the rear has been locked up. As to WHY that is, well blame it on the engineers error-proofing it for soccer moms, soccer dad's showing off and hillbillies. I believe thT one or two folks have soldered in a resistor to trick the BCM into thinking it was always in 4Lo