If you're towing with an automatic, you may want to look into transmission coolers to prevent the transmission from overheating due to the added weight saddled onto your truck by the trailer. If you're hauling a large trailer stocked to the brim with heavy objects then this may be a necessity.
Other than that just make sure that your automatic transmission fluid is at the correct level and make sure that you don't shift into Neutral whilst going down steep hills as this may adversely affect your ability to quickly shift back into Drive should you require more throttle (i.e. evasive maneuvers).
Have a safe and fun time on your trip!