Skyline gts-t not running properly

It boggs sometimes around 4-5000 rpm, does not feel as quick as it should be and it almost sonds like boost leak.(air hissing)

factory boost gauge only goes to about 4-5 out of 7

aftermarket boost gauge reads .8 bar, everything is stock so this seems odd

spark plugs are clean and nearly brand new NGK iridiums…

Air filter is dirty, i will change it tomorrow and clean the MAF

Any ideas what could be wrong?

I have a feeling its a boost leak or the factory BOV might be leaking

hhhhmmmmm, i would suggest,checking for a boost leak then…