Hi John Juma,
As you mentioned "problem comes back after 3 or five days with the truck working & need one hour to restart the machine again and it works"
=> Basing on the principle of the steering system of this truck model and my experience, I assume that you should do the following steps to find out the main causes:
1) 48V Contactor K7- the small one located under the display area: try to make the bypass or change the new one to see. This is because when the contact tips of this contactor are worn out it can cause many problems.
2) The Rim bearing / Ball Bearing the big one located underneath the drive motor (D~300mm) => check & see if it is worn out and blocked. Due to this is the main load of the steering motor so if it is so hard to turn => Will cause the steering system to be overload and make it crazy
Hope it helps
Good luck