One useful result of this thread is that it helped me learn more about our truck - and although most of you folks using the Duramax already know this, I've just learned that our new-to-us Duramax came equipped with an Eaton G80 locker. Sheesh! It's pretty obvious in hindsight. Check the glove box codes & know what they mean. I sure didn't know that.
As usually develops in an open forum there have been numerous thoughtful opinions expressed. Among them, "2WD = 1WD; 4WD = 2WD," etc. The value of the open conversation is that it helped me think through what I might do again - recognizing as was noted previously, there are scenarios that can trap just about any type of drive - I'll add, "Including tracked vehicles."
1) if we replace our current TV maybe a brutally efficient 2WD tow vehicle with a differential locker would be a good choice. This time we would know why we are doing it.
2) if we were stuck again I think I would use Paula's "orange lego" technique anyway. Either 2WD, locked or not, or 4WD has the potential to pepper the front of the trailer with shrapnel. "Let's not do that."
3) if we weren't towing perhaps the locker could be useful. Using forethought to stay in the "98% of the time I don't need it" is more attractive. If we inadvertently encounter a little slip 'n slide we now know our equipment better.
4) Ah! the unexpected. With leaves, etc., perhaps it's possible for us to carefully drive out.
Here is a link that was helpful:
This shows why the locker may work but the 100rpm differential between wheels can put some yuck! behind the truck.
5) and Thanks! to all for a stimulating exchange.