I towed with my 2016 F150 XLT 5.0 for the first time last week. 4000 pounds flatbed trailer weight, 440 tongue weight. I have an aftermarket Class IV hitch. The truck and trailer sit dead level with this setup and I experienced no swaying, braking issues, etc. The truck pulled and handled great.

I did experience some vibration between 55 - 60 mph going up and down steep hills when the road was exceptionally smooth. Otherwise, the ride was smooth with no issues. I was running the rear OEM truck tires at 40 psi vs 36 psi. This sounds like a tire balancing issue to me, but I'm interested to hear what you more experienced towers have to say. What about having the trailer tires balanced?

 

I always balance trailer wheels...