My 2020 F150 5.0 has the 10 speed (F550 was a 6), but as others have said, the 10 speed in the F150 can be shifted fully manual, or you can also use the plus/minus buttons to lock out gears in auto so it will only upshift to a certain gear.
I only tow my 5026 pound Ford tractor with the F150 on an aluminum tandem trailer and I just use tow haul mode in automatic. Seems to work perfectly for me. It will downshift for you when braking to give you extra engine braking.
I've read lots of horror stories about these Ford/GM co-developed 10 speeds, but mine has worked flawlessly so far.
With the Ford on the trailer I am grossing 12,808.5 pounds.
