Car studders around 5 psi boost?????

[Ry's_95tsi]

On the highway cruising last night i was going along 65-70 and when i would kick the turbo in (stock) to around 5 psi it would go for a few seconds then studder and loose power. but if it would studder and then i floored it so i was boosting 14psi it would not miss at all.

Here are my mods if it helps
buschur 2.5 dp
test pipe
hks hi power 3 in. catback
hard uicp
apexi bov
injen intake
8.5 super conductor wires
new plugs ngk

can anyone tell me what could be causing this or what i can do to fix it.
Thanks,
Ryan

 

[1stGenGSX]

probably a boost leak.

 

[eclipsegsx9797]

check boost leak, and your spark plugs

 

[Ry's_95tsi]

whats the best way to check for a boost leak?
is this robbing power from the top end too even if it only does it when held at 5psi?