1994 GMC Sierra Shifting problem

The truck is shifting late through all gears but seems to get better once it's warmed up. I thought it was the detent cable and have heard that the detent cable is a non-factor because the tranny is "elctronically controlled" where is the part located (and what is it called) that controls the shift points? Is it near the nose of the transmission on the drivers side? (round with a screw holding it into the tranny and a wire plugged nto it)?