'89 Dynasty Won't Shift into OD

My '89 Dynasty (3.0, automatic) won't shift into OD. I had the tranny replaced by a tiy mech w/40 experience. The used tranny came with a computer box (I don't know the technical name) that he put on it and since it didn't come with a filter he put a new filter on, too. That didn't help at all. What could the problem be? Thanks.

My '89 Dynasty (3.0, automatic) won't shift into OD. I had the tranny replaced by a tiy mech w/40 experience. The used tranny came with a computer box (I don't know the technical name) that he put on it and since it didn't come with a filter he put a new filter on, too. That didn't help at all. What could the problem be? Thanks.

Had the same problem with a 89 newyorker . First make sure all the wires are pluged in . there is a small one way down on the front corner thats easy to miss (i did) and after you check all that you need to discont the negative to reset the computer and teach the tranny to shift . if you have the owners manul it will show you if not you start out in 1st then shift to 2nd then to 3rd and OD then back down . Do this about three timesand your done . I hope