loosing power at 5000rpm

[Hicks]

If its loosing power its running rich. Specially if your running more boost than stock, you need a computer to fix the fuel mixtures.

I'd say its been doing it since the boost was wound up, but you didn't notice cause the car felt faster. but as time goes on and the car starts to feel slow again you tend to notice every little increase and decrease in power.

I've been there.

Get a S-AFC

or power FC if you have the money.