If you got 27 in it you don't have a 26 gallon tank. It shows empty well before it actually is on almost all cars, one reason for this is so you never run the tank so dry that the pump is not submerged. The fuel actually cools and lubricates the fuel pump. So a 32 gallon tank probably only has 29 usable gallons in it, maybe a little more or less depending on how the internal structure is chambered. It all depends on how much it takes to submerge the pump, and if it was designed in such a way to keep from running itself dry.