Should I rebuild my trans before we take trailer out west ??

Have done regular maintenance and run lucas additive. I have a 2000 gmc sierra with 300,000 on the original trans no rebuild, but the suburban has been towing a lot. I guess if there were signs of it slipping or other issues. I just have a hard time rebuilding when its not broke yet. But do not want to deal with getting fixed on road trip. You see why Im torn ?!?