Usually fill up around 1/4 of a tank, however there have been a few times more recently that I have allowed the level to slip to 1/8th of a tank, my problem is - the Truck only accepts 26 gallons of fuel. Am I an idiot or am I missing something. Truck is supposedly equiped with a 34 gal. tank - 1/8th would equal 4.25 Gallons. If my fill up only takes 26 gallons, where the *!*!* is the other 4 gallons?