Zero Niner, patch v1.4b extended the range of TII's to about 3000-meters, but still not the correct range of 5000m.
There's a small patch to fix the range, at Terrapin's site (
http://U-Boot.RealSimulation.com) in the SH3 Mods 'general-section'. The filename is: T2RangeMod.rar
It's an older mod but works fine with SH3 v1.4b
The mod is setup to auto-install the torpedo fix (file: torpedo.sim) to your SH3 folder. I think it's better to backup the v1.4b torpedo.sim file 1st, extract the mod to a desktop-folder, then install by hand.