i just drove from the east side of az to santa barbera about a month ago, no problems, kept it around 70-75 the whole time. the fluid change is a good idea to do about a week before your trip for a few reasons:
1) the obvious.. cars run better and more efficiently with clean fresh fluids.
2) while your under the car doing draining and and what not, it gives you the opportunity to inspect, things and possibly find a obvious problem or something that may become a problem in the future.
3) the reason i say do it a week BEFORE the trip is to guarantee that the new fluids are taking well to the yota and there are no leaks... example: the day before a trip i did a tranny flush and discovered that i had a small coolant hose that was leaking (small leak). went all over town looking for a new hose but everywhere told me it would be 3-5 days because it was a specially formed hose (it was). so i said screw it and figured how much could it possibly leak. make a long story short i got about an hour from home before ka blewy and hot (BRAND NEW) coolant went all over the engine bay. i was able to find a hose and jerry rig it to get home, but the new coolant was waisted and my trip was canceled. so that being said if you do things a week in advance you have time to work out the bugs (and get parts apparently)
.. p.s. another funny story, my friend got his oil changed at walmart while shopping for supply's for his trip a few years back. he bought his stuff, got in his car and got on the road. it only took him about 20 min to notice the sever loss in power and then that the oil light had come on... who knows when. he pulled over, car stalled and he called me.. i arrive to find his motor.. well F**ked. it turns out that some minimum wage walmart mech forgot to tighten the drain plug.. fried his porche boxter. oh yeah and because walmart is NOT a porche certified service center his warranty was void.