Hi Andy - I recently had the Nismo plenum installed in my R32 GTR. It's running -7's with forged internals and Haltech Pro ECU.
I initially had an issue in the lower RPM range (0-3000rpm). It felt restricted like there was insufficient pressure, so I had to keep the RPM's up or it would almost stall from a normal moving off or reversing.
It was a little like a Ram Jet. Seemed I had to be moving to ram the air in/increase pressure.
Glen at ESP managed to tune the issue out for me, and it is more responsive than previously (ever).
Result of installing this plenum: More kw's with less boost and earlier response.
Maybe worth touching base and having a quick chat.
Cheers
Richard