what kind of differential was put into the 2+2's?

[86 maroon gp 2+2]

I'm a dummie and don't even know what differential my grand prix 2+2 has, I'm pretty sure its stock but what gears and is it a posi or not? I keep seeing numerous 2+2's with posi units and I'm wondering if mine has one to

 

[pontiacgp]

if you don't know then you probably don't know how long it's been since the rear end oil has been changed. When you take off the cover to drain the oil you can check to see what you have for a diff. Good synthetic fluid in the rear end can not only make it last longer it can give you a few more HP and increase fuel mileage.