I have not had my EcoBoost to the Rockies but as far as engine braking goes it is better than any other gas engine that I have used, including a 460 and a V10. I do use mine to haul a much heavier trailer around some hilly country roads and the engine braking works very well for me. The first to second jump is a little large and some have complained of weakness in braking in the 30 to 40mph hour range. The main thing on engine braking is that it is most effective with the engine revs in the upper end of its operating range. If you are not getting effective engine braking but cannot downshift without overrevving get on the brakes firmly until you can downshift the let the engine do its thing. It is always better to be slow going down a hill than even a tiny bit too fast. Another suggestion that I have is to consider your trailer brakes. With a 6500lb gross trailer weight I would guess that you have two 3.5K axles. You may want to consider upping at least the rear axle to 7 or 8K brakes. I specify the rear axle because I am assuming that you have daisy chained leaf springs and they transfer most of the weight to the rear while braking. Stronger brakes on the rear axle may let you turn up the gain on your controller to save the truck brakes. I admit that I am alone on this but I feel that with daisy chained leaf springs your rear brakes need to be stronger than your front ones. I put a resistor on the front axle brakes of my equipment trailer and can run higher gains now without skidding the front tires of the trailer and have much better braking than I did before. The only issue is that on long grades I could overheat the rear brakes but the hills here are short so it is not too likely. Another option for the trailer is electric over hydraulic disk brakes that cool much better than drum brakes do. Here is a kit for improving your trailer brakes that might fit your trailer, others are available: https://www.etrailer.com/Trailer-Brakes/Titan/T4843700.html
There are a lot of bolt on upgrades available for pickup brakes as well. They are not horribly expensive and may help with your piece of mind. A 2014 truck may be about due for new brakes anyway. I just did my 2013 model.
