I have never towed with an Ecoboost but I have been towing with my 2005 Dodge Quad Cab (before they were Rams) 5.7 Hemi with 3.92 gears and it pulls very well. My Hemi only has 345hp and I believe 375ft lbs torque but the newer Hemis have more power. The only complaint I have is 2nd gear on the 5 speed transmission is geared a little high and doesn't keep the Hemi in the higher RPM range as I would like. From what I hear the 8 speed transmission is much better. The 5.7 Hemi has been around since 2003 and is a very durable engine. I have 97,000 miles on mine and have only just changed the oil, tires, etc. No problems with it at all and it still has a ton of power.
As others have said, the current Ram 1500s have coil springs which seem to have lowered the payload capacity so that will be something you will have to keep in mind. My 2005 has leaf springs and the payload is just above 1500lbs which works well with my TT loaded at around 6000-6500lbs.
Burch