Tim, maybe you got confused, the 4th gen tanks are 15.5... (and i think later 4th gens were 16 or 16.5)

i was pretty sure 3rd gens were 13.5 tank and like 1 gallon extra through the lines and neck etc. 4th gens i think were right around that. There were rumors of a "1le" tank that held more for racing but people argue about that a lot, some say it just had baffling to prevent fuel starvation.

Quick Google search brought up 14 gallons for third gen gas tanks.....

- Justin