I have used a Transfer Flow tank on both a GMC Duramax and an 8.1. I have not had a Titan tank, but the basics are the same.
The fuel gauge works about the same. For instance my Transfer Flow tank, when the gauge reads full the tank will be full, 1/2 the same etc. Where it changes is with my tanks (45 gal, short box) is when I have about 10 gallons left the low fuel light will come on rather than I believe its 3 gallons in the stock tank.
The fuel flow meter works the same between the stock tank and the larger tank. If I use 40 gallons out of the tank the meter will still read the amount of fuel use as it would in the case of the orginal tank (in my case my fuel flow meter is about 1.5 gallons light, I merely add 1.5 gallons to the meter reading and things are pretty close.)
I tend to use the fuel flow meter more than the tank reading because it is more accurate as far as I am concerned.
I do not use the fuel remaining feature because it will not function properly.
Having the range is always great especially when we are on the road for long overnight runs.