Id say fuel pump is on its way out.
Do you know what power you have? much mods done, and what boost?
I know my old r33 had the dual voltage sender for the fuel pump/sender. I had it removed and had it always on the higher voltage.
Id get it to a dyno/workshop so they can run it on the dyno and diagnose it properly.
If fuel pump is failling, the motor can lean out.
I had this issue, I had a195rwkw on 12psi, standard fuel system....within a month or two it ran like you said, took it to another workshop - Unigroup, and we had it on the dyno and found the cause.
Hope this helps,
Cheers,
Chris