WD5000AAKX on a SATA1 (1.5Gb) controller

I suspect that WdSSpd modifies 1 or 2 bytes in the firmware. By comparing the firmware modules before and after applying WdSSpd, we could determine exactly where the changes are written (probably module #02).

You could retrieve the firmware modules with the following tool:
http://sediv2008.narod.ru/Easy3.9Password01234567890.rar
http://sediv2008.narod.ru/Settings.rar