Alan,
Excellent Job!! First time I have heard those types of trucks called a "Shifter" Truck but so many names are used to describe them I will add that one to the list.
In Norfolk we just called them "hostlers" (even though that is really the job description of the driver) however I have also heard them called yard goats, spotter truck, and yard truck as well! It just depends on where you are!
I may have to commission you to scratch build some Flat Racks for me in the not so distant future and add another piece of intermodal equipment to your body of work!
Ed