[Citan]

I can think of 2 things ... 1 ) Turbo starting to spool (though I doubt it as our torque peak comes lower than that)

OR) Torque converter lockup, at a certain speed your RPMs will drop a bit, though your car will still pull


Basically when the output half of a torque converter(IE to trans) (laymens terms) reaches, or nears the matching input half (IE from the engine) the converter locks up, to keep from slipping/direct more power to the wheels

If you want more info on it, let me know...