Some tips to people starting out in Derail Valley.
the real money is made hauling between stations and hitting the time bonus. However the Shunter is going to have a hard time because it's lack of power will make it stall out and overheat up hill.

The solution is link 2 together. In the back up engine get is going to about 2-3 clicks in on the throttle. This will bring you to a speed safe for most turns and it will never overheat. Drive from the front engine and bring her up to the speed limit. At worst you may need to slow down a bit uphill to cool, but since you have two engines running your air breaks re-pressurize twice as fast giving you more control.
Just remember to watch the map and slow down near turns. When you get near the drop point shut down the backup engine before you get into town.