I did a search and couldn't find any info on maintenance recommendations for a positraction unit. The owner's manual didn't help. The dealer says I didn't have to do anything until 100K miles. Any suggestions??

 

There is no special requirements for your diff. The G80 diff isn't really so much of a friction type posi as it is a gradual locker. The G80 is actually a gov-loc differential and although it isn't as robust as either a genuine posi or a locker, it does well in stock application.

I just serviced the rear end in my Bravada a few weeks ago. Have a read through my writeup:
Rear Axle Service

 

Thanks. I did see your service info, that's what I'll do. If you have a moment can you explain a little more about the G80 diff? How does it differ from a "real" posi unit? Isn't the name positraction just Chevy's name for a limited slip diff? Does the G80 use clutch plates and such and require a special additive to the gear lube?