Originally Posted by VegasHB

Wouldn't it be the opposite? You would want to lock up the center diff more so you'd want to go to a heavier oil? This would help keep the front wheels from unloading to easily and "diffing" out.

When the oil is too lite in the center diff the power gets transferred to the path of least resistance which is typically the front wheels under acceleration causing them to just spin. This sounds like you're making the front work more but what you're really doing is causing power to be transferred to where there is no traction.