I have been looking a lot to try to find out exactly what I have in my car here and what it came with from the factory.

But now I'm curious what differential(s) comes in a '89 10bolt?

Before I thought it was the 9bolt, then I checked the vin, and it came with a 305tpi, so I'm at least certain it has the 2.73s according to speeds-rpm-gear.

 

As has been said many times before, why don't you perform some more-than-likely overdue maintenence and change the differential fluid and find out what you have while you're in there??

 

It was recently changed I just let a shop do it when I was too lazy.

And I was more curious as to what model they used, I already know it locks, 2 tire marks not one.