I towed a light weight Samurai on a 14ft tandem axle trailer with my old 04 1500 4.7 QC 4x4 w/3:92's and it was a pig in the numerous mountain ranges here in Nevada. Running near redline pulling the grades. But on flat or relatively flat ground it did fine.

The big thing is there isn't a whole lot of difference in fuel mileage between the 5.7 and 4.7. To me, getting the 5.7 is a no-brainer as far as the older trucks if you plan on towing. I know the newer 4.7's have more hp, so no doubt are better than the earlier ones. Although I have no experience with them.