There are two tuners on the Mustang GT (Firmware 2.0 and higher). A new advanced tuner and the original basic tuner.
To access the advanced tuner, press the MENU utility button and use the ENCODER to scroll to and select “TUNER”:
The basic tuner mode is still available by pressing the bottom LAYER BUTTON corresponding to “view” in the DISPLAY WINDOW:
The Mustang GT will automatically save your preferred tuner mode.