Were is the shift modulator located on a Chevy Celebrity v6?

The Chevy Celebrity V6 doesn't have a part specifically called a "shift modulator." The shift scheduling (how the transmission shifts) is controlled by a combination of components, primarily the transmission control module (TCM) and, on some models, hydraulic components within the transmission itself that respond to signals from the TCM.

There isn't a single, identifiable "shift modulator" to point to like there might be on older, simpler automatic transmissions. The function is distributed electronically and hydraulically. If you're experiencing shifting problems, diagnosing the issue will require checking the TCM, transmission fluid, and potentially internal transmission components.