VW Lupo 1.4 TDI: Engine Problems & Performance Issues

Hello.

I'm not entirely sure about this topic, and I also can't find any other measurements from engines with the same specifications to compare with.
"In addition, the entry I'm looking for is missing from the table titled 'Target values for measured data' for the AMF engine."
I am sorry, but I cannot access external websites or specific files online. Therefore, I am unable to translate the text from the provided URL.

The following problem:
I don't notice any significant turbo lag in my Lupo, but I'm also not sure if that's how it's supposed to be. I bought the car in July 2014 and have been driving it since then, with a fuel consumption of approximately 4.0 - 4.7 liters.
I don't have much trouble overtaking, but it's difficult to reach 140 km/h on the highway; I can only go faster downhill with a tailwind.
In addition, the MSG is displaying the following error: "Vacuum pressure limit exceeded."

I then conducted a test run, and during that run, I noticed two unusual things:
1. The target air mass value at full throttle (1000mg/H) is never reached; the actual value is always a maximum of 850mg/H.
The value is already quite close, and I simply suspect that a target value is set based on the air mass. I've also read that this target value isn't used to control the engine itself, but only to adjust the EGR valve.
I adjusted the air-fuel mixture tightly, resulting in a measured air mass of 410-460 mg/H at idle.

My question regarding this: Is the measured air mass value plausible?

2. The target boost pressure is reached very slowly. In my Passat TDI with an AVF engine, I'm used to the boost pressure being regulated very quickly. It's a VTG turbocharger, so that's how it's supposed to be. However, with the AMF engine, it takes about 11 seconds to reach the target boost pressure. Is this normal, or is that why I have an error code in the engine control unit (ECU)?

I have already carried out the following investigations/measures:
1. Air filter replaced.
2. Intake manifold cleaned on the engine.
3. EGR valve closed.
4. Catalytic converter to muffler, new (due to corrosion).
5. Vacuum measurements were performed.

For point 5, I proceeded as follows:
1. Directly after the air filter, a pneumatic fitting was installed at the mass airflow sensor. I connected a differential pressure gauge (Testo SmartProbe) to this fitting.
During the process, I clearly measured an increasing negative pressure, with a maximum vacuum of 50 mbar between the charger and the air filter.
My guess is that the air intake is blocked, which is why I might also be experiencing a loss of power.

But perhaps my assumption is completely wrong, and the set of measurements I took is perfectly fine.
Unfortunately, I can't assess that myself, so I'm asking for advice.

Perhaps someone else who has also performed a dyno test (003-008-011) with their Lupo AMF, which definitely shows no issues, would be willing to upload the results?

Thank you very much for your help!