I don't believe the truck was overloaded, with no suspension mods, fully loaded w/ camper there's still a lot of clearance from the frame to the axle and the back still rides 1" higher than the front. However I do believe the Firestone design is not appropriate at least for this specific F150 2016 application; the brackets end up being the axle stop unless high pressures are used. To get a reasonable bracket clearance requires at least 50 psi which ends up with a compromised ride and a very high back end.
Fully loaded with the Timbren SES severe duty kit there is still some clearance between the rubber spring and the axle "pad" so there's no load riding on them.
