Also agree with above. With dp/rp OP should be seeing about two psi more boost. Hope he has a boost gauge or will get one if he mods.
As to "uppin" boost, 18 psi sustained on the K04 is about all it will handle before turning into a pure furnace just making heat, no more power, and roasting its tiny and frail center shaft to failure.
Keep sustaned boost to no more than 18, with maybe occasional quick peak to 19, but not at more than 6,000 rpm, or join the zoom, zoom, boom club.