This can be quite a tricky fault to fix. Is your car a GT model with the 280 hp motor? Your car sounds like it is going into limp mode. This is easy to establish as all you need to do when you get the fault is switch the engine off and start up again. If you get full power back then the car was in limp mode. The problem with the GT model is there is not many Nissan specialists who can fix this fault as it is not a common model. This could be an air leak in the system, air flow sensor fault, turbo fault, oxygen sensors fault, gearbox sensor or throttle sensors faults. Most likely it is a throttle sensor fault or air leaks in the system. It is a total nightmare to fix as there is usually no specific fault code. I am in NZ as well give me a call on 021654446 and I can give you a more detailed info on this fault.