12 bolt limited slip posi, is it factory?

[bucky_21_7]

So over the summer i jacked up my rear end to see if I had a posi without taking off the rear end cover. I spun the wheels and they spun in the opisit direction.So seeing that i presumed i had no posi, just peg leg. Today I pulled off the cover and found a limited slip posi ( not the clutch posi, the spring one) sitining in there. Now the question is, is the limited slip factory? The rear end gears are 3.08's. I read unless stated on the options list that factory atomatic trucks are 3.08 gears and 3 and 4 speeds are 3.73 gears. Am I right? My truck was a factory atomatic truck so the gears are right but is the limited slip? There is no indication on the option list of it. If not where did it come from? Thanks