Update:
Sorry its been a little while while I try to sort this out.
I did a few things:
I bought a scale and weighed my tongue and then all wheels as well. I show 6300 pounds on the wheels and 1000 pounds on the tongue. My scale may not be perfectly accurate, but should be close enough to judge percent. that is 14 percent on the tongue after all I have done, and loaded as traveling other than food and a few clothes. the food goes over the axles in the fridge so that wouldn't change much, and we only bring a few clothes at a time.
I added a second sway bar. that didn't seem to help anything.
Next, I removed the rack on the rear bumper and spare tire, and relocated the spare under the bed. that probably gave me another hundred pounds to give the 1000 pound tongue weight. I didnt use the rack anyway.
I also read somewhere your truck tires play a big role, and on another forum it was mentioned certain Wrangler tires are not suitable for trailer towing as they cause sway since the sidewalls are not steady. I don't have that exact tire mentioned, but I do have the Wrangler fortitude tire. To make the best of it I did raise the pressure in all 4 truck tires to 50 PSI, just shy of the max cold pressure. I figured this was good since with a 1000 pound tongue weight and about 300 pounds in the bed along with 2 passengers, we are looking at the full payload of the 2019 F150.
I will consider if I should buy LT tires next time and see how those work?
I gave it a go and it was so much better with more air pressure and perhaps shifting about 100 pounds more to the front by removing the rack.
It is still not absolutely perfect, as with a little wind it is still a little unsteady, but at least it is not constantly moving the truck around on the last trip and I actually could get up to 70 mph this time on the interstate with no constant side to side. I am not sure if the weight was the thing (as it was always within 12 percent before moving the tire and rack), or the tire pressure, but between both it made a noticeable improvement.
Mark Newbill
RE275
2019 F150