help please diesel experts turbo boost problem

[jebiga41]

Am really stuck here and this is completely wrecking my head am running an aaz with a KKK14 turbo was working fine till i fitted a chargecooler which leaked so have stripped it all out and back to a jx inlet manifold with the BOV taken out and blocked by a bung all surfaces gasketted properly and sealed hoses in good condition am now using the jx short inlet hose. Engine boosts up to 3/4 bar max but normally only runs around 1/2bar boost but keeps losing boost around 1/2 bar of boost pressure usually around 3000 rpm any ideas guys really stuck as am meant to be going to coney farm tomorrow thanks in advance.