Unless they've changed it in the MY07 with the 2.5i... and maybe it's different with the GT.
I can use my auto 'boxin four modes: I will call these modes "full-auto", "auto override", "sport" and "full manual".
Full-auto: self explanatory. Step on the accelerator and brake, let the car do the gears. Don't touch steering wheel controls. Computer is smart, human is dumb.
Auto override: as above, but you can change gears with steering wheel controls. It will go back to full-auto if you have light throttle on, and will shift before redline.
Sport: Similar to full-auto, but it shifts at a higher rpm and gear kickdown is two gears, not one.
Full manual: Start off in Sport, and then change gears. Sport light should turn off. It drives as close to a manual as you can. It will stay in the gear you assign it, and it *does* hit rev limiter and will not change gears for you.