Thanks, I was going to crawl under there and look but it was raining when I posted lol. I did some more web digging and found replacement diff covers that say the the axles are AAM (American Axles Manufacturing - I think). The front appears to be 9.25 if the replacement cover I was looking at was correct and the rear is 11.5 14 bolt of the same make (AAM). It appears that these are the same axles used by GM in the duramax.
I would still like to know if there is some sort of decoder ring for the build sheets