Some top brand batteries will last 6 or 7 years but they do not have the strength at 6 years that they did brand new..Take it to a small battery shop and get it load tested..Or you could buy a jump starter pack to take with you..Sears makes reliable ones..
It doesn't matter what shape the rest of the truck is in if you have a weak battery. Your getting near the end of it's life, if you were staying local it would be no big deal to stretch it longer. But why take chances with your trip. We all know how quickly the weather can change out West. Change the battery for your own peace of mind. Enjoy your trip!