Hey man.
I am guessing you are talking about an R33 gtst.
The stock boost controller is controlled by the ecu, and there could be a variety of things causing it not to go into high boost.
I personally couldnt be bothered trying to figure it out, and instead removed the standard boost controller, which gave me 7psi, all the way through the rev range.
have a look on the forums, in regards to disabling the standard boost controller. from memory it was something like shorting out the black wire to ground, which sends a signal back to the ecu. don't qoute me on that, but have a look on the forums, and you will find the post.
If your temp gauge sits half way or there abouts, your temperature should be ok. And i doubt that the temperature would affect the computer boosting.
And man, dont feel disheartened by this, it happens to all of us, i know how i felt when mine melted a piston, but now that she's all good again, i realise whyh i love it so much hehe.
You'll get it sorted.
Hope this helps.
Cheers maka.