Hi friend,
You can't hear and u can't count the speed of the motor pump I am really sure you can't unless u have speed-meter or Still Sted software....Therefore, pls. do what I have told u before than let wait and see...my friend...
PS: Technical side is not by feeling (my friend) unless u have a very long & good plus experience...

Thank you for your reaction.
You mention "the speed of the pump seems to be reduced". The speed of the pump is not reduced. It looks like the speed of the pump correspond with the position of the joystick, but the valves are not activated.

Hi,
- Can hear the electromotor running also accelerate and decelerate depending on the position of the joystick => the control system should be no problem but the speed of the pump motor seems to be reduced by unknown reason.
- When the truck is powered for half an hour it runs fine => this means the hydraulic system is OK.
=> I used to face a similar symptom in the past: Just open the control panel (display) to look for the battery 3VDC then replace it with the new one. This battery is responsible for feeding the power supply for the microcontroller of the display and it would be ready when the key switch ON. If it is over, when you turn ON the key SW the controller needs to wait for a while to warm up the controller, in your case is half of hour then it is ready for use.
Just try it and let me know the outcome
Good luck