Mitsubishi, 1988 , Mighty Max - Pick UP

4 cylinder
90m original miles
automatic transmisson

Trasmission will not shift correctly -was told by a tranny shop tech it was the governor.

I believe this is a jatco tranny

I am trying to avoid the tranny shop cost for repair .

Question ? ---where is the governor "located" and is it difficult to replace . I am a fairly good mechanic but not a tranny wizard.