The 5.0 is a solid engine with good torque and hp numbers.
5.0 specsIt is a simpler engine than many out there, no turbos and no direct injection. For all the concern you hear about turbos I think direct injection is more likely to cause grief as the miles add up due to dirty intake valves*. That being said I choose an EcoBoost, but I am towing heavier than you are.
MikeUp pulls 6k (3.73 rear end if I am not mistaken) and is happy with the rig. PickupTrucks.com also likes the 5.0. With 6 speeds to choose from in the transmission I would not sweat that you have a differential that is at a lower ratio.
As mentioned a couple of times check the door sticker so you know the payload. If you can get an integrated brake controller they are really nice.
Good luck to you,
Stu
* Yes, my 2012 had the condensation problem with the intercooler. Ford's solution was less than optimal in my opinion, they reduced the efficiency of the intercooler by blocking off a portion to reduce the condensation. I have not noticed any performance impact due to this change and it resolved the issue.