Epic Weapon Specialization
Type of Feat: (Epic) Combat
Epic Weapon Focus (chosen weapon)
Weapon Specialization (chosen weapon)
Specifics: The character gains a +4 bonus to all damage you deal with the chosen weapon.
This feat can only be taken on a Fighter, Champion of Toran or Champion of Vorax level-up even if the Player Character meets all the stated requirements.
This feat stacks with Weapon Specialization, for a total of +6 bonus to damage.
Not sure where your seeing Greater Weapon Focus and GW Specialization, but i cant find it in Lore nor in my NWN players manual. There is a Superior weapon focus but this is a Weapon Master freebie feat upon attainment of lvl. 5 WM.
I copied the above from the Layo Lore pages.