Rugging at full load start

Moin Moin, I drive a Nissan Micra k12, bj 2006, 1240 ccm, 80 hp, 223000 km. When starting with load, i.e. if the most gentle pedal kick is not being hit, the car breaks. Mainly in the range of 1500-2500 revolutions. This runs through all gears. Due to the feeling of lack of force lock I wanted to change the clutch today. However, the workshop staff said that this is intact. This is also unlaudable, because the switching processes are clean and partly a clean pull up is possible. Especially in the morning, i.e. with a cool vehicle, there were no restrictions. It is now assumed that a sensor, the control chain has also excluded the workshop master. However, he could not yet tell me a concrete idea. The car goes to the workshop again on Wednesday to read out. Does anyone have an idea in which direction the search should go? VG and many thanks already in advance in advance.