i've read some threads that mentioned that evo won't pull as hard after 5K rpm?

is this true? if yes what can cause this? boost limit? i know that the peak is around 3500 rpm.
i've also seen some dyno results and after that 3500 rpm the curve start going down...

any good explanation?

sorry i am not a turbo expert, in fact this is my first turbocharged car. what can i do to fix this? ECU re-flash?

 

The boost drops off after about 3000-5000 RPM. It's just how the computer controls things.

Get a computer upgrade (whether it's flash or piggyback, plenty of threads on that subject) and it should fix most of that feeling.

 

The Boost fall is a small portion of the loss above 5K. The biggest issue is the air/fuel mixture the stock ECU runs. The car runs supper rich above 5K which is dropping power. With a S-AFC you can gain back over 30 WHP with re-setting the mixture.