Not using tow haul is hard on the brakes, and it can affect performance a bit. It’s not really detrimental to the transmission however. The 5R and 6R110 adjust line pressures based on shift speed and slip anyways. So... it’ll compensate for the weight being moved. That’s why rental and fleet trucks can feel too snappy when you first hop in.
Also Intermotive used to make a module to make Tow-haul the default. At some point Ford made that a settings option. At least as far back as 2015. U-haul also has tow-haul set as default.
