I've seen this feat before, but I can't find it anymore... All I remember are the following qualities:
- I believe it was a feat, though since my memory has failed me in other areas, it might also be a Rage power
- It allowed you to spend 3 rounds of your Rage in order to gain a benefit
- I believe the benefit was extra damage on a single attack
I originally found it on the German Pathfinder PRD, which shouldn't be all that different from the english counterpart. Either way, the German version doesn't include a large variety of books, so I don't imagine it comes from a very exotic edition.