Your bumper isn't the only thing to consider when hauling a heavy load. Another important factor is your truck's power. While many trucks have the ability to haul a trailer, some have a special tow/haul mode that helps you tow heavier objects safely.
The tow/haul mode changes a vehicle's transmission shift patterns. Pulling a heavy load requires a lot of power. The tow/haul mode reduces shift cycles. Depending on the truck, it may also boost torque and engage an engine braking mode to help drivers maintain control while driving up and down hills.
In general, the tow/haul mode changes shift points to higher RPM limits. This helps you keep moving as you haul your trailer. As you go down hills, you may notice that your transmission will downshift earlier than normal. This allows the transmission to help you slow down and saves wear and tear on your brakes, too.
Many manufacturers design the tow/haul mode so that it disengages a vehicle's overdrive feature. Shifting frequently can cause overdrive to burn out.
Check your owner's manual to see if your truck has a tow/haul mode. If it does, consider engaging it when you need to haul a heavy load. It will help you maintain control of your vehicle and trailer and cause less stress to your truck's transmission over a long haul.