Wire length increased and now it runs in rewerse when I pull the throttle?
Is there any logical explanation to this - other than I have swapped two wires?
Had a look at my steering servo. Its a Hitec HS-645MG. Would the digital version of this servo (that you mentioned) be able to turn the wheels when the truck stands still or is movement of the truck simply a requirement with this size of RC-car?
You swapped two wires during the process. About the extended motor wires- longer motor wires are not as big of a deal as longer battery wires, although it is best to have the shortest wires possible. The 5645MG is much stronger than the 645MG, you should be happy with it.