Hmm
when I first got my R32 - I used to get this quite badly too. I figured it was fuel related – it seemed to surge (continue to drive or accelerate) when I lift off the throttle at speed (freeway driving).
Just by way of a process of elimination for you, I've done a full engine rebuild, new R34 N1s, new plugs, new fuel pump (Tomei), new Spiltfire coil packs, new SX fuel regulator, new fuel filter and I've even had my std injectors cleaned and flowed. (not just to fix this problem – obviously)
Since I installed a PFC with the matching EBC - the problem is much better - which is to say that I still get it - but only very rarely, and no where near as bad (the passenger can not notice any more).
I told my tuner that I was having this problem (when he was installing the PFC) and he said he could tune it out (he seemed to have heard of this problem b4). The car also used to hunt @ idle (and even stall some times) – but the PFC has fixed that too.
So - I suppose what I'm saying - I'd be interested in figuring this out too