I tow a 17' travel trailer wityh a 405# tongue weight. In the manual it says a WDH (weight distributing hitch) is required for over 300#. I use a double round bar WDH with 600 pound bars, antisway bar with stock suspension and tires. I have experienced one time any "bad manners" from other vehicles. that was a Chevy Surbaban.
On the trailer forum for my brand trailers there's a thread about just this thing and it seems that a 45 degree gust or wind, from the left or right front side, is what causes problems and it also cuts fuel mileage if it's a continious wind. I have BFG Long Trail T/A tires that have a 50 PSI maximum inflation and run them at that when towing.
I believe unless you have worn parts, I'm at 56k miles, when your properly set up for your load and tongue weight no other suspension parts are needed. this subject comes up reguarlly on the trailer forum too and the "air bags on their F-150" users usually come around to the fact that a WDH is worth the cost in ride and handling.
Hitched up the rear of my liberty is 1 inch lower using a WDH.
Check your WDH for proper set up
