You'll have no troubles towing that trailer. I'm pulling a trailer that dry/empty starts at 5400lbs and is 28' coupler to bumper. You'll need a WDH. I've always had good luck both renting trailers and now owning with the Equalizer 4 point sway control. about $675.

 

1st of all, sorry for such a big picture. I don't know how to resize.
I have a 2016 F150 FX4 5.0 w 3.55 rear axle.
Also, added shell, front and rear bumper, winch, wheels and tires, decked storage system.
Now, let's see if I understand this correctly. According to my sticker, my combined weight of gear should not exceed 1880 lbs. So, if my trucks capacity is 7000 lbs, I have to weigh the truck, subtract the weight from 7000 (my CCC).
Now, I've been told that my truck can conventionally tow 9000 lbs. That's w/o a WDH. I've also been told that I would need a WDH to tow the 9000 lbs. Both were from different dealers. But the hitch says 5000 lbs max with 500 lb max tongue weight. Do I need a WDH to tow 9000 lbs?

 

Short answer yes. Longer answer will be provided by other regarding your numbers/math as far as what you can and shouldn't tow, stay safe out there!

 

Forget the 1880 on your payload sticker. Adding a bunch of stuff to the truck, changing tires and rims, etc, has made that number menaingless.
The 1880 payload is "as built" when it left the factory with a full tank of fuel.

Please read the towing guide for your year including the footnotes specifically this one.
"Addition of trailer tongue load weight and weight of passengers and cargo cannot cause vehicle weights to exceed rear GAWR or GVWR".

In other words that 9,000 pound tow rating is with an as built truck with very little besides the driver and a WDH.

7000 - truck at scale = remaining payload.
This will give you an idea of what you have left for towing. I suspect not much.