Power Loss: Causes and Solutions

Hello!
Last week, I had a new head gasket installed in my Golf 4 (model year 2001) with an ASV engine and 110 horsepower.
(High water loss, high pressure in the cooling circuit)! However, before and now, I have very little power at around 1950-2100 RPM. Especially accelerating is quite difficult; it feels like there's a delay between pressing the accelerator and the engine responding. Above the mentioned RPMs, the power is normal or even more responsive. I cleaned the turbo and VTG during the head gasket replacement, so I can rule those out. I temporarily replaced the MAF sensor, but there was no improvement. A short-term increase in fuel injection didn't change anything, and the fuel injection start is also fine. I'm actually out of ideas; maybe someone here has a suggestion!
Sure, here's the translation:

"Thank you."
best regards

Hello,

How many holes did the old head gasket have, and how many did the new one have? Switching from 1 to 3 could cause a moderately noticeable effect.

"It's more likely to me that the modifications caused leaks in the vacuum system, which may now be affecting its performance. Please check the measurement blocks 8 and 11 to see how the boost pressure regulation is working in the relevant speed range, for example, with the full throttle setting between 1200 and 2500 rpm."

Quote:

I cleaned the turbo, or rather the VTG, at the same time as the Zkd replacement, so I can rule it out.

That's precisely why I wouldn't rule it out.
Is the VTG can installed correctly? Unfortunately, the holes have some play. Hopefully, the VTG rod hasn't been tampered with.

Best regards, Rainer.