Which version do you have? I have had the fuel tank parameter for awhile, but I was one of the beta testers for it, if I am not mistaken, it is released to the public now. Go to the hptuners customer login, v2.1 is now up on your download page if you upgraded to usb, if not you will be able to download 2.0.18 which also shoudl have it. All it is, is a parameter that is supposed to calibrate the fuel guage to the actual size of your tank, and now GM's "one size fits all" fuel tank calibration.
And for the saving, the individual windows will only save to a text file, and it only saves that table, so you can go into another file later, and upload the text file and you dont have to copy and paste. Really helpful if you are going to tune other people's vehicles and you just need one table, you can also keep a good database of tables this way. Thats what I do with it.
As for saving the whole file, the only way to do that is the save button at the top of the software, if you want to save it as a different .hpt file, you will need to do the save as function under the file pull down.
Chris
2009 Silverado, HPTuners, all stock.