So I just bought a G37s and in some gears it will hit the rev limiter at only like 4k rpms. Like yesterday I was leaving first gear and it just started banging off the rev limiter at 6k rpms. The other day I was in probably like in 2nd gear accelerating, then it just hits the rev limiter like ba ba ba ba ba at only like 4k rpms. What could be causing this???

Sounds more like a garden variety misfire-under-load than rev limiting. Have you scanned it?