You may be making the wrong assumptions about Fords F150 gvwr packages between 2014 vs 2018. They really haven't changed that much looking at Fleet Ford specs.
First off The F150HD package has a 7850-8200 gvwr depending on year model...and a 4800 rawr LT E tires. This is the only HD payload package.
Next down is a 7550-7600 gvwr and 4550 rawr with P tires.
On down is a 6900-7050 gvwr and 4050 rawr with P tires.
And a 6750 up to 7050 gvwr with very small 3800-3850 rawr with P tires.
Ford markets a max tow in all the above configurations. This confuses lots of owners.
Fleet Fords specs shows 3 different frame thickness..... .87"t.... .10t and .110t.
Ford shows 2 different size brake systems.
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Axle mfg rating are always higher than the truck makers RAWR.... trucks RAWR is the lessor of a tire/wheel or rear suspension. Upgrade to a higher capacity tire means the wheels and rear suspension needs help also.
Like others say just stay under axle/tire ratings for a safe tow.