With all that payload why would you need some type of helper spring?

 

Even with a HDPP a loaded bed squats the truck a lot. Mine are 3/4 of on inch off the axle empty and with 750 lbs in the the timbrens just barley touch the axle. Or for and example, a empty 7x14 dual axle empty enclosed cargo trailer squats the truck by 1/2 inch with no WDH installed.
So the timbrens with a HDDP add a extra cushion of safety. Once the trailer is loaded and hitched up properly (WDH) it eliminates the up and down motion of bumps and swaying.

 

With 17-1800 pounds of pin weight + passengers and extras in the truck you're going to hit the bump stops or come very close even with an HDPP. I measured mine at 1/2 inch from the bumps and had a slight bit of sag on level ground.
I didn't feel unsafe and the truck can handle the load. I had a decision to make:
Airbags (and all of the fiddling around that those can bring)
Helper spring (and the extra stif ride you get when empty)
RAS (At the time I ahd not heard much on the RAS, what I had read and heard was good and this was/is my fallback)
or the Timbren/Sumo Spring route.

I went with the Timbrens.

I'd rather hit the progressive rate helpers in the form of Timbren SES a bit sooner and have a level truck than sag and hit the factory bump stops when I hit some nasty road.

Like jeffinthbag said, just an added cushion of safety (and control)

 

I’m surprised that the truck drops so much. How much suspension travel does it have without Timbrens?

 

From the above post, 1/2 “ to the factory stops, so I’m guessing not much left.

 

I never measuered it.
I know I'm pushing max rated limits on my truck which is why I don't reccomend hauling a 5er with an F150 UNLESS it's an HDPP, Going up to rated limits is not an issue for you, and you know what you're getting into from an operator perspective. This combo is not for everyone but it works for me.

An F250 Gasser or F350 Diesel would be a better fit if just looking at ratings or you're new to towing.

 

I frequently fly an aircraft within 2% of its limits for work. I’m good with doing it to a truck. :-)

 

2% of VNE, among other things?

 

Yup. Air Ambulance. We don’t worry about the fuel bill so much.