Something weird at 3500-4000 rpm

[Bunta]

Ok so here it is, when i start to floor the pedal (happens on every gear) and the rpm goes up, the boost kicks in, and right when it hits 3500-4000 rpm the car all of a sudden bogs, chokes, lags, or almost dies (the feeling is like when it's your first time driving and you really haven't learned how to balance the first gear yet, so it chokes and nearly dies), so then i just shift to the next gear and it then it seems fine again. It's like the car can't go past 3500-4000 rpm.

It's weird, to me but hopefully not to you guys.

The car does have a pretty big leak coming from the turbo manifold gasket.