I guess it depends on what you're looking for in a power train. I'm looking for fuel efficiency and towing power, not 0 to 60 power; sounds silly to say it that way but there is a pretty big difference to me anyway. I don't know off hand if the 5.7 hemi will beat the 3.0 DM in 0 to 60, probably closer than we think. But I'm willing to bet the 3.0 feels stronger while towing. It probably just continues to pull and pull without having to downshift or wind up.
My trailer is not overly taxing my hemi, for the most part I sit at 2300 RPMs on the freeway, but onramps and passing truckers, I hate that it has to almost redline so often. The sound is great, but part of me feels like I'm flogging it too hard at those times.
Unloaded though, yeah the hemi is certainly fun and makes passing people a joyful thing. Again sounds silly especially since I just said above that I feel bad working it hard while towing, but the difference in my mind is that when unloaded the hemi scoots like a scolded cat whereas loaded it just revs and revs and sits there; all show no go. I get it, I'm pulling something heavy so it's expected, but that difference is why I prefer the diesel if price and rest of the truck is all the same of course.
Whats your MPG unloaded with the diesel on 100% highway? Some guys are claiming they can get 30+ mpg which is awesome.