Found this in my '01 owners manual
You can pick up the PDF version of the owners manual here:
https://www.mygmlink.com/main/US/en/gm/home
Shift Light (Performance SHIFT Light)
This light is used for performance driving to indicate
that the vehicle’s best performance level has been
reached to shift the transmission into the next higher
gear. The SHIFT light will display at an engine
speed of about 5,750 rpm, just prior to reaching the
engine fuel cut-off mode. To better understand the
vehicle’s power curves, see “Capacities and
Specifications” in the Index.
Don't know if it in the same section for your year, but try page 2-113.
It would be cool, but I don't think it is an option in HPTuners or LS1 Edit to be able to set this.