well first thing i would do is check your ignition timing... make sure it's at 10 degrees with t & e1 shorted in the diagnostic box
next thing i would do is check all your vacuum pipes and intercooler pipes... make sure you don't have a leak... this can contribute severly to underpower
what boost are you making?
i wouldn't panic bout the bhg just yet.... do the other checks first
most likely cuprits = turbo to intercooler pipe coming straight off the turbo
lmk how you get on