I was experiencing some issue with engine low power

Hi, I am having Hyundai Atos Prime GLS, 2010 model, but driven only 40000Kms. All service history is perfect, company made. After my last regular service, which was major service, I was experiencing some issue with Car power. It is not going more than 100km/hr speed. When I returned back to them, they told everything is normal. But seriously I am feeling that the car is not having power as before service. Also feeling that the Engine is struggling hard. Also the Engine noise also got high. Before the car goes to 120km/hr without any issue. Now it will not reach that speed in any case and the engine sound is also high.

All service history is perfect, I was experiencing some issue with Car power. It is not going more than 100km/hr speed. When I returned back to them, they told everything is normal. But seriously I am feeling that the car is not having power as before service. Also feeling that the Engine is struggling hard. Also the Engine noise also got high. Before the car goes to 120km/hr without any issue. Now it will not reach that speed in any case and the engine sound is also high.
What could be the issue?

What could be the issue?

Rgds,
Siva