Man, some great continued comments, so thanks for that.
Re the AFM/DFM issue - DFM issues are starting to crop up (and I'll admit I don't know the frequency or numbers, as I think it is new enough technology that no-one really knows at this point) and I just prefer to steer clear.
I am not brand loyal (have owned a Ram truck, a Ford truck and two GMCs), so will go with whichever one gives the best option for our current and anticipated needs.
Re "overkill", I've actually mulled over the Ford 7.3 more lately and am starting to look more favourably at that.
And, regarding travelling speeds, currently, due to the wife's work commitment, travelling (in normal times) to see our grand-daughter in Denver, means that our time is constrained, which requires as few days driving as possible so visit time is maximized. It's 24 hours driving time one way, done over three days, so no dilly dallying. In a few years when she retires, the situation will be more relaxed. So I am looking at a new vehicle which can handle that work, among other attributes.
Marv