Hi James.
You may be on the right track when you mention fuel. The hardest the fuel pump will ever work is when the throttle is wide open and the motor is a high RPM. If it is hesitating when you're asking it for max effort but it is going ok when you just crawl up to high RPM, it could well be the bad batch of fuel has clogged your fuel pump or filter.
Have you tried changing the fuel filter? Are you able to have the pump flow tested? If they are a boot install in the R33 it may be worth your while to remove it and have it checked. As you mentioned, it could also be a clogged injector, but you wouldn't expect such a pronounced effect if only one was clogged.
If you DIY as much as possible, you'll save lots of money. Last weekend the radiator in my 626 daily driver busted itself (top tank cracked). I took it out myself, had a workshop repair/clean, the self-install and saved around $300 in labour.
As Chris mentioned above, it could be a coil pack. Do you know how to test your coils?
It's down to process of elimination dude That said, I had the same symptoms in my 180SX years ago and it was a cactus fuel pump.
Cheers
Mark