I know you guys wouldnt usually go onto the silvia forum, but this thread is worth a look, it's not always a majorly technical problem, i'm not saying that the avcr isn't faulty or needs to have the duty retuned i'm just saying it's far easier to eliminate the simple things first.
After all the concept is the same,
The car in question was a 180sx, it had upgraded turbo with the additional bolt on's that come with it, it had similar problems to what you are having with your gtr, the guy spent a lot of money replacing things having things retuned etc etc, when in the end it was just......
read this:
http://www.nissansilvia.com/forums/index.p...=132004&hl=