I have a chevy 2500hd 6.0 gas which ias a little down on power to the ford. I am actually out camping right now. I towed here at about 16-16.5k combined which is about a 9-10k trailer weight.
It would hold 70 mph on the interstate the whole way here through the hills and mountains of western virginia and west virginia.
It went up the afton mountain grade at 70 mph and 4500 rpm. Afton mountain isn't that bad of a grade but is a pretty good example of a typical interstate grade. 5% or so and about 6 miles long. Good enough grade that the big rigs are in the right land going 35 with the flashers on.
It will go the speed limit or better on pretty much any road I have taken it on in the eastern US. I am not sure what more one could ask of it power wise.