Newbie Driver Mercedes Actros Low Power on Hills

Well the truck arrived this afternoon. My brother was able to figure out what was the cause. There is an economy/power switch. (He thought it maybe just driver error). This switch has to be pushed when approaching a hill. You have full power then. Also the truck can run over the limit (100km/hr) when going down the other side. If you have it in economy it struggles to go up the hill, but, maintains the limit going down the other side. This switch seems to disengage once cruise control is activated again. So, push the button again when approaching another hill...etc. Well, this is what he seemed to have worked out while driving this vehicle on his second day. Maybe there is another way to do this? We will have time now to get familiar with this type of beast.
First thing now she is home is to have a good service so we have our own record starting point.
The dealer was not able to pass on any history of the previous owners service records. This would contravene the "privacy act". Yeah, I can see it.... one law will contradict another! So, bugger the safety aspect of having a history of service/repairs to a machine. You have to trust for the sake of someone's privacy...!

Thank you all for your time and attention. I hope to give you some more updates as we learn more about this truck.
I have attached a photo for all to see.