Ya' know, it popped into my head overnight that my 2017 F150 with the "Max Tow" package can handle a 12,500# load, but it has three options on the shifter for the 10 speed transmission - OD, Tow/Haul, and Sport. The Owner's Manual is clear that when pulling a trailer, or with a heavy load in the bed you're to use "Tow/Haul" to prevent damage. It keeps the tranny in lower gears, and the RPM's in a tighter range for Max Torque, all electronic. OD shifts out to keep RPM's low, and Sport keeps the RPM's above about 2000 so the turbo's are spooled up a bit, ready to kick in boost.

I'm thinking that your idea of running through your dynamometer climbs with a load is going to require more than just popping the tranny into OD and forgetting it when pulling a trailer. Again, I'm no tranny guy so I would be talking to some "experts" about how to get the most bulletproof package. Maybe there's someone here that hasn't chimed in yet but has some answers.