quote Koenma

I looked through ANN's Manga Encyclopedia and did not find an entry for a Gungrave manga. While that does not mean that one doesn't exist, there is probably a low chance that a Gungrave manga has been published, unless it is a doujinshi.

If I were you I would stick to the Naruto anime. The manga and anime have very little differences, and with the animation you have the added benefits of voices, music, and a new episode every week. VIZ is releasing the manga at a painfully slow rate, with a new volume every four months. At this point in time the anime is both cheaper and faster to follow. The anime should be caught up with VIZ's releases of the manga within the next two or three months.

quote Cloud Strife7

Why does it take so long? Rurouni Kenshin is monthly, so it's possible for it to come out fast.

quote Koenma

Naruto runs one to two chapters monthly in the English version of the manga anthology Shonen Jump. In order to keep the monthly releases ahead of the graphic novel releases, the graphic novels are not compiled until the ten-or-so chapters found in the original Japanese graphic novels. Most of the series running in Shonen Jump are released at the same rate:

Naruto
Yu Yu Hakusho
One Piece
Dragon Ball "Z"
Hikaru no Go!
Shaman King

The series (Under the SJ) not serialized in the monthly Shonen Jump anthology are usually released monthly or bimonthly.

quote SummonerSupreme

Also remember that the original Japanese dialogue has to be translated/adapted into English. That takes time as well, plus Viz is extremely horrible about putting out new material in a timely fashion.