Holy cow....looking at Fleet Ford specs shows a 2018 F150 SC 4wd... tiny 3.3 V-6 engine...6500 gvwr and really small 3350 rawr.
Just sayin' but this truck will struggle severally trying maintain speed and pulling grades due to the small hp/torque 3.3 v-6.
The biggest safety factor is those tiny 3350 rawr that will be carrying the load. A super crew F150 4wd rear axle may weigh in the 2300 lb range....1640 plus 2300 = 3940 lbs for close to a 600 lb overload on the rear axle. The weak link on the 3350 rawr can be the rear axle assy....tires....wheels....rear spring pack. That particular 3350 rawr is good for around 1000-1050 lb payload.
AS other posters say that small 3.3 will struggle but may or may not be a issue with you.
You may have to address upgrades to that tiny 3350 rawr....but is doable if done right.
I see a better truck for towing in your near future.