To correct the speed signal, a module under the dash must be replaced. It is called a digital ratio adapter and it modifies and sends the speed signal to the other modules that use it. A different part number is required for different axle ratios or tire sizes. Your dealer will be able to determine which module part number you need. Secondly, pulling a trailer puts a lot of stress on the rest of the drivetrain.
Heat is the big killer here, so keeping the engine and transmission cool is the next priority.
Towing in overdrive puts extra heat into the transmission because the torque converter has to work harder and generates a lot of heat. Finally, make sure both the truck brakes and trailer brakes are in tip-top shape. Trucks that are factory equipped with towing packages typically have bigger brakes to handle the extra stopping loads.