I don't know if it is still true, but in the past first class awards on US came from the same bucket as upgrade seats, so you can see if the usairways.com website will let you book a first class award on your flight. If it will, then there is an upgrade seat. It is a bit voodoo, since they will make more seats available as the day of flight draws closer, so it is quite possible that they will move seats from the F bucket to the O bucket late one night and you will get upgraded an hour or two later and never have seen availability in any tool.