That's really odd. Did you pump up the tubes outside the tire (pump them til they bulge) and put them in water (bathtub) to check for leaks? If a tube won't hold air, it HAS to have a leak or a bad valve (at least logic tells you that, and real life isn't SUPPOSED to defy logic). If these take 5 minutes to go flat, it's a slow leak and will be hard to detect. Leave the tube under water for several minutes and look for just an occassional bubble. If all 3 bubble in the same place, you'll know whether to look for the culprit in the tire or the rim. Check the rim carefully to see if there might be a metal sliver or a spoke sticking through that is damaging tubes. Maybe replace the rimstrip. Check the tire again (I know, it's new). If you find the cause and can keep the tire inflated for 24 hours and can ride it once before the race, then I think you can stop worrying. Otherwise, maybe you could borrow a wheel from someone? Hope this helps. Good luck.