It would be boost cut.
You can fix it with either a piggy back like the standback, or you can buy a boost cut killer.
See:
http://www.mpsgarage.com.au/shop/pro...t-killer-.html
I highly doubt you have hit fuel cut at 4000rpm...
I will almost guarantee that if you put a boost gauge on it, if you put it in a high gear and load it up, then the boost will spike out of control till you hit a cut. Everyone thinks its fuel cut, but in fact it's boost cut.
Just be careful, if you fix that and your car isnt setup properly then you will have bigger problems...
My advice: slap a standback on it and get it tuned. Then you know exactly what's going on and there will be no surprises.
CorkSport FMIC with Cold Air Induction, , Cork Sport Cat Back, CPE Standback with PNP, TurboSmart BOV, Custom Highflow Cat with CorkSports Downpipe,Pauter Rods, CP Pistons,ARP Head Studs, BIGGER TURBO COMING, Pre-ordered a Stage 3 CPE Engine.