limited slip diff Q

I have always been told and been under the impression that if you had an open rear end in your truck and you had the rear wheels off the ground if you spin a tire by hand the other will turn in an opposite direction.
If you had a posi or limited slip of some kind both tires would turn in the same direction.
Is this true??
I tested it with my Tj with trac loc and sure enough both turn the same way, open the rear to change fluid clutches ok
In the 99 tahoe the tires turn opposite.... Ihave my window sticker I paid for limited slip.
Open the cover to change fluid... see clutch packs, looks like a posi.
There is no tag for modifier or anything on the cover, I am the origional owner.
Is it wrong about the tire rotation, or am I missing something??
any ideas?? advice
Thanks all

if the trans is in Park, the wheels should go opposite directions.......but with resistance usually..