...to woods and pike....to carify, BOAZ is referring to the icon of the REAR diff. The 4x4 info screen graphic has an icon for both the center and the rear differentials. Jog your memory, was the center one showing locked, or the rear? ....or both? I doubt Boaz is wrong on this one otherwise the display would be meaningless.
...as for the full-size spare being a tell whether or not the rig is equipped with the HD package, it would depend too on whether it is straight from the factory or if the dealer/previous owner had time and/or opportunity to switch the spare one way or the other.
All of these things put together would pretty much tell you one way or the other:
1. Check the spare.
2. Go drive in Rock Crawl up a hill and look at the display.
If you have the fullsize spare and the display shows the REAR diff locked, you have the HD. If you do not have the fullsize spare and the display does not show the rear diff locked, you do not have HD.
That ought to do it.