Hi ,
I'm having the exact same problem, you should read this Thread
"GTI cutting out, oil light flashes"
it's 18 pages long but it is very relivant to this issue, lots of people having this problem.
Mine is the same problem, the engine starts to cut, if I manage to get the clutch in quickly the engine
will cut out sometimes jumps to a start again and revs up to around 2k and cuts out again, after a few seconds all is calm, and I can usually restart first time.
I have the fuse box panel cover removed at the moment, I can hear relays gogin mad, flickering, when this problem occurs. I've pretty much done the very same things you have so far, just replaced my fuel pump relay, but not convinced it's the colution... I'll post an update very soon,
Other suggestion have been, Speed sensor relay, Ignition coil may need rewiring, ignition coil may not be getting enough power, have a read through that posting.
The VW fella is correct ,. it's as common as hell ot seems for GTI golfs 8v's, pity VW havn;t got it sorted.
I've yet to see a definitive answer form VW poeple, RAC people.... so the saga continues..
good luck
N