OK, before getting a (apexi Super AFC used for adjusting A/F ratio's about $700 bucks? not sure)
Try turning your boost down to about 12psi, In most cases the standard turbo on an r33 will not run efficiently at 14 psi and may even produce less power at 14 psi. Untill you get you car dynoed at the different boost levels you wont know for sure but i would run 12 psi for now to try and resolve your flat spotting.
Also see if you can get that stock BOV to try and solve your starting issues.
If turning the boost down does not solve your problem it could be that one of your coil packs are shagged :-{, once again getting one of a mate to do some tests would be your best bet as you dont want to waist money buying coil pack (about $125 sh)...