My Commercial Level A340-300 creeps really fast when at idle. I take my foot off the brake and it starts off briskly down the tarmac and I have to keep hitting the brake. Is there some control in the aircraft.cfg that I can adjust to slow this down? Otherwise, it handles great.

You could edit the weight and payload section of the aircraft.cfg but can just do that in the weight and payload section of FS when you set the flight up. Increasing the payload will make the aircraft heavier and has usually solved the problem for me.