TDI Engine Problems: Troubleshooting & Repair

Hello fellow enthusiasts,

I have a TDI engine, model BJC, installed in a forklift. The engine drives a hydraulic pump via a toothed belt. A bolt detached from the input shaft of the hydraulic pump and wedged against the housing, causing the engine to abruptly stop.
Even after identifying and removing the blockage, the engine still wouldn't turn over. The diagnosis was a bent crankshaft. So, the engine received a new crankshaft with new bearings, as well as a new flywheel. Everything was assembled, and the engine starts perfectly and runs normally at idle.
However, here's what happens: when you rev the engine (without a load), it starts to shake noticeably around 1900 RPM, and the shaking subsides again around 2500 RPM. At 2600 RPM (which is the maximum it will rev to), it runs normally again.
There is also software (from the manufacturer) for diagnosing the engine control unit, and there are no error codes stored.
What is noticeable is the regulation of the injection start. Initially, the pump is close to the optimal operating point, and the operation of the injection control valve can also be clearly heard during the actuator diagnosis. At idle, the actual value still follows the target value (around 7.5 degrees before top dead center), but the regulation only works up to just before the aforementioned approximately 1900 rpm. At that point, the target value is 0 degrees before top dead center, and the duty cycle of the injection control valve has reached 2%. Immediately after that, the engine starts to shake, and the actual value then fluctuates between 5 and 9 degrees before top dead center (while the target value remains at 0). At 2600 rpm, when the engine is running smoothly again, the target value is still at 0 degrees, and the actual value is approximately 9 degrees before top dead center, with a duty cycle of 2%.

"Furthermore, during the shaking process, the injection amount fluctuates between 0 and 20 mg. However, I assume this is due to the control system's attempts to maintain a stable speed."

To be honest, I have my doubts whether this is really the cause of the shaking. In a brand new vehicle of the same model, the ESP, MSG, and ESD modules have already been temporarily replaced with new ones, but the behavior did not change.

Does anyone else have any ideas? I'm really stuck and don't know what to do next.

Best regards, Frank.