Turbo lag/Revs dropping

[Derbados]

Hi all newbie here hope everyone’s good! Looking for a bit of advise, admittedly I don’t have much mechanical knowledge so any help would be greatly appreciated!

I’ve got an issue with my 2006 connect 1.8tdci, in third and fourth most noticeably when the turbo should kick in around 3/4k revs the revs dip as does the power and you have to put more gas on it will get passed that point then it’s ok again. I’ve had it plugged into diagnostics and it was clear, changed the fuel filter and had an engine carbon clean, it hasn’t improved it, anyone else had similar or know of any fixes or does it sound like the turbo is shot!?