You'll get more out of a custom tuned ECM over something like a harness module that Banks offers. As always, that depends on the tuner itself but usually the custom tuned ECM will be smoother and more powerful.
I would image the dealer has all the service records on file for that truck, so you should be able to draw a conclusion from that.
Welcome to the forum!
I think you'll find most shop that "alter" parts will not really advertise that, or even want that activity referenced with their name.
But, good idea that can be used for sure.