This is what I found regards the Type IXD2, the source seems very reliable.
I checked the sim file and you are totally right since it got the right speeds but the wrong ranges, since it gives it a max surface range of 23700 @ 10 knots and 57 submerged @ 4 knots and they aren't within specs. To be honest, I do not play much with the IX2D so I didn't even notice it so if I would like it to be as realistic as possible then I will surely alter the file.
http://www.subsim.com/radioroom/albu...pictureid=3587
And while you are into it, check this site, there is useful info regards the engines used by american subs.
http://www.subvetpaul.com/Engines.htm