I've had exactly this just recently on a 2WD Cossie. Hard driving for a short while and no problem, then when turbo is hot, 4500 rpm misfire and won't rev any higher. Weirdly enough mine got slightly better on right and slightly worse on left hand bends.

Rolling road diagnosis told me that all the sensors are fine and the electrics are fine we now believe it is fuel related - pressure is good but fuel flow isn't great. So have flushed the tank, got new fuel filter on. Also checked fuel lines for proximity to hot exhaust.

Charlie