Andrew;
A serial number would help ID the changes in the power assist steering you truck has. Do you have the testing procedures for the electric assist steering by using the control module? In the base of the steering wheel gear box, truck's left rear, is a steer torque sensor that has three wires, and on some occasions a flat spot developes on the cam follower that is inside the box. This makes the steering next to impossible to neutrally adjust. The steering chain under the truck's battery can become corroded and cause overloading of the electric assist motor.

Hi andrew
Have you got an email address so i can send you the manual to assist you