I, just 1-month ago, bought my 2009 RAM 1500 w/HEMI.
I also own a 2004 Dodge Durango equipped with the 4.7L.
I can honestly say that the mileage is about the same between the 2 engines.
We've taken two trips in the RAM and I saw anywhere from 18.5 to 20.5
I've not yet pulled anything with my RAM but from the aspect of sufficient power, I'm not concerned.
I have towed with my Durango and wasn't impressed with its power. It would rarely allow itself to shift into OD.