I would guess one of three things. If you have a waste gate it could be weak and creating your small boost loss. Two, if it's a variable turbo could be the actuator or stuck fin. Three. Weak spring clap on a CAC boot blows open a leak at 40 then will maintain 35 psi but that would usually be accompanied by a squeal that sounds like a constantly slipping belt. Most likely am 05 will have a dual turbo set up that is waste gated and the waste gate is probably weak. Hope that helps.