To answer your question, the tuner can be set to whatever you want. It comes with 3 programs of your choice (93 performance/93 torque/87 mileage for example) 87/89/93 octane gas, whatever is available in your area or what you want to pay for (Gas price wise). Most gain will be seen from the highest octane gas available in your area. It will re-calibrate your PCM for larger tires or a gear change plus a lot of other things (Intakes, remove rev limiter, speed limiter and such). Also with the XCal-2, you can rear/clear CEL codes and you can also data log (using a USB cable and a laptop) your vehicle to see how everything is running and report back to Doug so he can tweak your files even more.
From the dyno run I have seen, the 93 performance setting yields about 17ft/lbs of torque at 2-3k rpms where normal driving is done. Each truck responds differently to tuning so it varies.
With the USB cable (Read FYI below), Doug can send you updated files and you can load them on your tuner yourself. No need to send the tuner back to Doug, much easier and faster this way. You can also edit your own custom files that Doug makes you (If you want to decrease/increase speed limiter, timing, get bigger tires later on, gear changes, transmission shift points, idle RPM, and more). This is probably the best mod you can do to your truck.
FYI: You can get any normal printer USB cable and it will work fine with the XCal-2.