If you have the heavy-duty towing package, you probably have an auxiliary transmission fluid cooler that also should be flushed.

One way to avoid an overheating transmission is by flushing and replacing the transmission fluid. Also consider installing an aftermarket cooler.

So a flush is a better alternative. We use a machine at the garage that connects to the transmission cooler lines.

Tech article detailing a DIY flush and fill technique for replacing automatic transmission fluid.