Alright, so after a bit of searching around this is what i have come to figure out.

-ZR2s have a larger ring rear diff
-zr2's may or may not have a g80 in the rear (why they wouldnt confuses me)
-I have read conflicting statments regarding the front diff, it is not locking but i have read that some zr2s may have an iron diff, while other statements say they were only available on the 5spds, can anyone confirm this (When i get a chance ill stick a magnet to mine).

So im going to have to go check the rpo code to make sure i have a g80 although im pretty sure i do.

Just from driving around before even reading about this (as i knew from the owners manual a locking diff was an option, so i assumed it would be in zr2 as that makes sense).
So from driving around i figured that it only locked at low speeds (Generally in 1st gear).
I figured this out after a few blown drifts at higher speeds when i lose the lock, although most of the time at higher speeds can manage to get both tires spinning (Even in a drift at about 80kmh)

Now heres the thing, I dont know how well it is working..........I know from driving around corners at slow speeds the back end will kick out super easy (suggesting a locked diff)..........in the summer i have seen a peel out mark from both tires (suggesting locked diff) as well as towing out a truck frame that was frozen to the ground in an impound yard that there was dig marks in the gravel from both rear tires.
So thats what is leading me to think its working (even at 200,000km)

Now whats making me believe its NOT working is.
I was in a snowdrift, in 4lo i got out left it in drive and one rear wheel was spinning at idle and not the other, same as the front)
I was in another snow bank/hill, while i got the girlfriend to drive and i pushed i could see that again only one front tire was spinning which is expected, but again with the rear tires one tire had a solid grip on the ground and was not spinning, while the other one was hung up and spinning a bit.
Which makes me think that it was not functioning to well.

Now heres the catch! Both of these times it was around -20 ish or so outside AND the blazer was only running for about, say, 15-20 minutes of driving max, so with the cold temps making the oil a bit thick would this impede the functionality of the locking diff.

 

My ZR2 had a aluminum diff. I found my G80 to work the odd time, but rarly did. It had 300 000km on it.

Oh... and you should buy a locker...such as mine...lol

 

Ha! I would buy a locker if i did enough offroading to warrant it.

Im thinkin the g80 is just simply not engaging properly when its that cold, either that or its a bit worn out and under serious load is slipping