Which is in effect, the FM 3-22.20 or the FM 21-20?

I've heard from NCO's and officers that the FM 21-20 is as of now obsolete, and replaced by the FM 3-22.20 I've seen tons of platoons left, right and center doing it, but not mine and I'm chosen to lead PT soon. Is there some policy letter or something stating that the FM 21-20 is obsolete and replaced by the FM 3-22.20? I've found a partial download of it, but it's missing the first few chapters. Is there a complete download somewhere?