I have a 2014 1500 with the 5.7 which works well for my particular needs, but if I required a 2500 it would be powered by the 6.4 simply because of the RPM power range. You will read of the recommendation for 89 octane fuel for the 5.7 but in reality you will notice very little if any difference in actual driving. Towing, both engines will provide average mpg of around 8 to 10 depending on trailer size. Empty both will average 16 to 18. We drove our 5.7 1200 miles over Christmas,from south of Memphis to Charleston SC to Raleigh NC and back through the Smokies. No towing and mostly highway speeds in mid 70's. Average fuel burn was calculated at 19.8. With 87 fuel. If your towing requirements are within the range of the 5.7 specs, you will be very happy with it. If you need. A little more torque, get the 6.4. You will certainly be happy with either.
