Is it normal for my battery gauge to fluctuate from 11 to 14.5 while driving?

11 volts seems a tad low with a load on, like lights, A/C, yet the question is how accurate is the dash gauge?
Do you have digital or analog style volt gauge in dash?
Having the voltage read while driving, by using an OBD2 scan gauge or even using a VOM from the battery or front 12v accessory port, may give you a more accurate reading for comparison.
Do your headlights seem to dim or blink at all at night when idling, indicating a lower charge?
Many alternators do not put out much amperage until you reach 1700+rpm, still the system should try maintain at least 12.5 volts and range up to 14.5 with higher rpms.
The good news is that you are under full warranty and you could express your concerns with a service tech, and have them do the tests and see if it truly drops to 11 volts while monitoring the charging system.
Also the battery should be properly load tested, with a pass or fail scenario.
If you were to leave your hood unlocked overnight, as to not open door to drain down anything, a good AM voltage reading at the battery, should be around 12.4volts.

Yeah, what Soft Ride said ^^^^^^ , voltmeter and all.

Either way, don't mess with it, make sure you can reproduce it, take it to the dealer, point and cry.

Yes, that is normal, since 2005, GM vehicles alternator output has been controlled by the PCM as a fuel saving measure. If the battery is fully charged, no need for the alternator to be fully engaged. The fuel it saves is probably infinitesimal, but it may prevent overcharging and frying a battery in very hot underhood conditions.In my experience with my 2005 K1500, around town it'* always charging 14+V, when I stretch it'* leg'* on a fairly long freeway run, it will drop below 12V.