Gas gauge and Miles to Empty

My low fuel light has been coming on when the trip meter says I have used 25 gallons of gas and the gas gauge reads about 1/8 of a tank. The miles to empty says about 40, but isn't counting down mile for mile as I drive.

When I have filled up, I have put in about the same amount as the trip meter says I have used.

I thought this truck was supposed to have a 35 gallon tank? There can't be 10 gallons of "reserve" can there?

I have only filled it up a few times since I only have 1000 miles. Is there some kind of self-calibration the system needs to go through with more use?

Is mine normal compared to the other trucks? I have a dealer appointment for Monday hoping they will find the computer is programmed for the wrong tank size or something like that.

Thanks,
Aaron