The Traction-Lok differential was available starting in the '81 model year. It was optional in '81 with every engine/transmission combination except the the non-turbo 2.3L w/ auto and 3.45:1 and the 2.3L turbo w/ 5-speed and 3.45:1. With those two it was standard. It was also standard with the 5.0L starting in '82 but still optional with the 4.2L.