With the v6, you can set it on 4Hi and drive it around just fine. The center diff is open and the truck is operating just like the v8's with AWD. Since the center diff is open it allows the front and rear drive shafts to spin at different speeds. When you lock the center diff, you lock the front and rear drive shafts together, just like traditional 4wd systems found on pickup trucks. You cannot (rather, should not) drive on dry pavement with the center diff locked UNLESS you will ONLY drive in a straight line (for very short periods). The traction of your tires will force the drive shafts to try to turn at different rates if you turn or travel in an arc. With the shafts locked together at the center diff/transfer case = bad news for your gears.
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