White knuckle is often the result of improperly set up trailer or inexperienced driver. You can be over your payload and not be "white knuckled"... and you can be way under your payload and be "white knuckled".
OP, without knowing all the details, many of us here believe that is too much trailer for your truck. The HD F-150 with Ecoboost is a great engine and strong platform, but you have a LOT of weight and wind resistance (frontal and sideways) from a 36 foot long trailer. The HD F150 is still a relatively light truck, weighing in around 5500 lbs or so. While you have plenty of engine to pull that weight, you don't have much truck weight to resist trailer push.
If you decide to tow with this truck, I hope you have a high quality weight distribution hitch and make sure that it is properly set up. If you don't have load range D or E tires, I would recommend them. Make sure to do annual brake inspections on your trailer and ensure they are working properly. Watch your speed, be careful in high winds and keep speeds down when descending grades.