I know the newer ones are, and I think the older models are too, but I couldn't find a definitive answer. I say yes, but not 100% sure.

Posi traction was an option for the rear dif.

If you want to know for sure if your truck is a SureGrip (posi) or not, jack up the rear of the truck, with the truck in nutral spin one of the tires, if the opposite tire spins in the same direction congrats it's a SureGrip (posi) if it spins the other way no such luck