I don't see why you should be too concerned about the trans, these are stout units. Drop the pan, replace the filters, put the pan back and re-fill the trans. You won't get the fluid that's in the torque converter, but that's not really a problem if you didn't already have a specific concern. if your 02 Overland is like mine, there's already an aux trans cooler on it.
My advice is inspect all of your suspension bushings, the repetitive jiggling of a sustained highway drive could be different enough from their daily "groove" that they finish dying at the worst time. Be sure they're in fair or better shape before you head out. If you have any vibrations or out of balance tires/etc, get that resolved before leaving. I drive commercially as a major component of my job (just drove from Phoenix to Chicago to Dallas in the past week) so the above advice comes from direct experience.