I found this on Youtube, and it's a pretty honest assessment of a 6.4: the comments are good, he lists the weights, and has a shot of his travel-trailer:

Towing

If you click on His profile, there is a comparison video to a Cummins and a video of the 6.4 empty mileage numbers.

I'm impressed with what I saw in those videos. This fellow is getting better fuel mileage out of a bigger engine, and a heavier truck than my 360 Mag with all the tweaks done to it for better fuel mileage.

And, like Him, I also owned a couple of Cummins diesels, and don't miss them one bit for the same reasons (see the "comments" section).