Hmmm.... I might be wrong, but could it be that you are only focusing your power on the down stroke? I learned that to pedal efficiently up a hill, you have to put strength into the whole pedal cycle. Don't just stomp down on the pedals... also pull up. Imagine scraping something off the bottom of your shoe as the pedal gets to the bottom of the stroke, and that should even it out. (Greg Lemond's trick, not mine!)

Let me know if that sounds like it could be it... Oh, and what's the ride? I'm looking for a metric century to do as my first organized ride too. I ride in CT often when visiting family.