I've been having that lag problem too.I first noticed it when I was in 3rd gear 4500 rpm and i floored it.it didn't want to go.lol.
The shop I go get my amsoil oil from has a dyno and the guy was like he can put it on the dyno and see if there's any problem with it.I've just been to lazy to bring it in

 

I'm not a mechanic and I don't know this car inside and out, but if you are in 3rd gear at 4500 rpm and go to the floor with the throttle it should not feel like there is any sort of lag unless:

1) VDC is kicking in for some reason
2) You are used to driving a GTR or a Lambo

I would also expect that if there was any issue with timing, fuel delivery, air flow, etc causing the lack of power then you should be throwing codes via the CEL.

If it was the clutch you should notice RPM's climbing and wheel speed falling off.