In terms of mpg (can't speak to reliability), you can see my mpg in my signature. I live in fairly hilly northern Virginia and drive with a pretty light foot. Roughly 70/30 city/highway.
It's interesting that your 3.6L V6 fuel economy (17.8 MPG) is fairly close to what Motor Trend got with their "Real MPG" testing. Not saying this is conclusive, just interesting and worth investigating further.
The 3.55:1 final drive ratio is a nice compromise between performance and economy, that's one advantage to the 3.6L V6 (5.7L Hemi available ratios are 3.21 and 3.92 for 2019 1500).
If someone is looking for fuel economy as a high priority for their use-case, it makes sense to me that a Hemi eTorque, driven with a light foot, would probably be the best choice, because that engine would nearly always be loafing and not stressed. Over the years, I have learned that it is better to have a little more power on tap and rarely use it, than to go with the low-end engine and have it working hard all of the time. Now, whether or not the Hemi eTorque would pay for itself in the long run, that's another story.
The other consideration is resale value...what percentage of people buying a used pickup are looking for a V8 vs a V6? The OP could go to KBB.com and check trade-in value for 2015 or 2016 Rams, identically equipped except for engine, and get a pretty good feel for whether or not the V6 is more of a liability or an asset at resale time.
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