ok, so I took my car out for a good thrash today.
when I was doing 55MPH in 3rd gear around 7000rpm. then I went for WOT hit 8500rpm and shift into 4th.
after shifting into 4th I was still doing WOT but I notice theres a power delay right after gear change for a good 0.5s the engine seemed like reduced power. after the lag everything was fine again.
it only happened after gear change when the gas was reapplied. no lag or power loss throughout the whole range of the gas was constantly applied.
I tuned off ESP and no difference at all.
I think its might be the intake and ports close and reopen switching between on-off-on gas situation.

 

YOU WERE SPEEDING?!
O:
shiettt you're crazy

 

no I wasnt speeding.

 

I have noticed this in my '05 as well. Not sure what the deal is. Best I can figure it's the intake ports readjusting themselves. Otherwise, I have no idea what would be causing it. I notice most when shifting aggressively between 2nd and 3rd after hearing the beep.