Well with any car,plane,ship that uses oil to power itself the range is very relative to many things. Of course the slower the rpms the better range but at the cost of ever getting there. For a sub youd would want to use the speed that gives the best of speed and the least fuel use or in TMO and RFB 9 to 10 knots. But you are never going to get the "max" range as things like charging batteries and using high speeds to set up post on a convoy are going to mean that you will never get the max range. But for me at least fuel has never been an issue so long as I run at TMO ahead standard the typical actions on a given patrol I often have 40% fuel left when I get back a little less if I was out of Pearl and had to travel to Luzon or something very far like that. Dont know about the range stats above for a Balao class I have seen places say a bit higher. But I have read that some time in 43' they began to fill one of the ballast tanks with fuel after some genius came up with a way to modify it and that all Gatos and Balaos at some point after this came about got this ballast tank mod which added some range to the subs. Safe to say that the Tenchs either where made with this ballast tank mod or they had more or larger full time fuel tanks.
http://www.fleetsubmarine.com/balao-class.html. The wiki data is most likely for a pre ballast/fuel tank mod Gato. In Take Her Deep the Hailabut had this weakness when she was in a 3 sub wolfpack the other 2 subs had the ballast tank mod she did not and had to leave a few days before the others to get home. It varied but the ballast/fuel tank mod easily added several days to a subs patrol time vs one that did not have it.