I'll have you know that I speak fluent sarcasm. Just ask the VP of HR.

 

As i am sure the op is already aware Setup is key with the wdh. Make sure trailer and truck are level. Like mentioned earlier what are the measurements of the front wheel fender unloaded,loaded and with wdh engaged. Your goal is to be half way or 3/4 back to normal with wdh engaged for most setups. Also with a trailer that has a gvwr of 9900lbs. It sounds like new tires with 10ply rating are in order that are capable of 80 psi. This stiffer sidewall will help tremendously. I tow a camper similar in weight with a equalizer 14k hitch. Its rock solid my guess is hitch setup issue

 

How many miles on your truck tires? On rare occasions you'll run into a set of tires that feels squirrelly until you get a few thousand miles on them. Problem is you can't tell if the tires will act that way until you try them. Let me tell you, it is a scary feeling.

 

^^^^
Are you sure your tires are fully inflated? My sticker says 70psi front 80 psi rear, not 65...
I also agree with others that you NEED a weight distribution hitch. No question about it and it needs to be set properly.

 

smlford,
I just checked my 2017 F-350's sticker and it says 60 front and 80 back. But I have 18" tires. Maybe that's the difference between mine (60 psi) and yours (70 psi).

 

If you're using a 2"-3" adapter for your hitch receiver, DON'T! Get a 3" hitch stinger. There is a HUGE amount of play when using the adapters. Play between stinger & adapter + play between adapter & hitch can play havoc with a weight distribution/sway control.

 

MY GVW is 9200 and when we go camping on the beach I wouldn't doubt we're there plus the stuff loaded in the back of the pickup. I have air springs and WDH and once I hit the combo setup right, it's good to go.
Your GVW is 9900 period....not far from mine. You have an F350 mine is an F250, you should not have this problem.

 

Get the alignment checked. My 250 showed no signs of it being out but with the trailer I could barley stay in the lane. Toe was way out on both sides and correcting it fixed the problem.

 

I know you looked....
My 2017 is taller, you checked level trailer to truck? Not taking to much weight off hitch?