Hey guys,
Newbie to this forum but regular user of the UK forums.
Had this same flatspot on my 33, would hesitate and verge on stalling everytime I went to pull away. Checked for leaks, cleaned the aac etc etc etc.
Turned out to be the O2 sensor was shagged, changed it for a generic 3-wire one and it cured it instantly.
May or may not be your solution but worth a try I reckon.