Umm, there seems to be alot of confusion in this thread in regards to the Trigun and Trigun Maximum mangas.
Heres the story.
Trigun was first serialized in Shonen Captain magazine from the series debut in 1995 until the magazine was cancelled in 1997. Following the cancelation of Shonen Captain, Nightow changed publishers to Shonen Gahosha and the series continued to be serialized in Young King Ours magazine. Due to the original publisher retaining the name Trigun, Nightow had to change the title to Trigun Maximum, which isn’t a sequel; just a new name for the rest of the same series.
So, technically, Trigun Maximum just continues the story that started in Trigun. The manga is different from the anime, because around episode seventeen or so of the anime, it had caught up to the manga, and after that, the storyline greatly differs becaus the anime had to come up with an ending.
I heard there would be a Trigun movie in a couple of years, though.