> ... a differential lock in the rear differential ... would
> make the truck nearly as capable as a 4WD.
This is not really true. My truck has Detroit automatic locking differentials
front and rear, and the rear differential does make a substantial contribution.
But without the front axle engaged, it is not nearly as capable. Also,
without 4WD one has no low-range gearing, which is critical to off-road
driving. In addition, locking differentials have quirks that can be dangereous
on the highway; this can be overcome by practice or by using a
manual-engagement type. And by the way, the remark someone made to the effect
that "4WD only gets you stuck farther away" only applies to unskilled drivers.
