Hi! Your tank has exactly 38 gallons capacity Even if computer says its 0 miles, you still have about 4-5 gallons in it thats right. I have 2008 F250 with 38 and once after computer said 0 miles i got almost 100 miles more Mine is 6.5 diesel and i have approximately 17miles per gallon.
Richard,Europe
(You can get the 60 gal main tank and 40 auxiliary if you want from one Cal company only not sure about what the law says about it at the place you live