And enter the noob................
hows it goin, new to this, so be gentle..... he he he...
if your running standard boost, and you've added the new exhaust and front mount etc, you could be experiencing boost creap which is comon.. i found my r33 would sputter and fart at higher revs though until i put in a fuel cut defender and re gapped the plugs..
the FCD helped a fair bit but when i regapped the pluggs that made a world of difference..
the re-gapping of the plugs is probably the cheapest spot to start... i'd then suggest a run on a dyno after that and maybe fuel filter as well to determine the problem properly.. but i do understand that cost presious precious cash monies to do this.....
any ways, couple of extra ideas for ya... hope it works out and the problem gets solved...
nothing worse than chasing a bug...