Got a 4wd question

[91z71]

A little back story, I got my truck stuck yesterday, really bad. Snow was up to the bottom of the doors. I was trying to get some speed to pop over onto the trail which was a good 2 feet above the ditch I was in and kept sliding over, eventually wedging me in between the trail and some trees.

Here is where it got weird. I was trying to rock myself and get the front tires back enough I could go back into the clearing and get away from the tree and only 3 tires were spinning, like they should, considering I have a corporate 14 semi floater with a g80 in the rear end. But, when I engaged 4-lo all 4 tires were spinning like the front diff was locked. When I popped it into 4-hi only one of the front tires were spinning?

So, unless chevy put some fancy dancy front locker on a truck that engages in 4-lo, then that tells me something is going to fail in the near future. I guess I'm just asking, what could cause that? Not really a huge issue, just curious is all! Thanks in advance!