I hear it's bad for the torque converter to rev it lots in neutral - is this the same in Park?
I thing the main advantage of the Italian tune-up is to run it under load for a long time - I don't think it would be as effective running at high revs in '3' than in 'D' or 4th, as the engine would not be under very much load.
Maybe you need a big hill to run it under load without exceeding the speed limit too much..
2.5-16v 1990 90,000m Astral Silver
2.0E 8v 1986 107,000m Black