As the original poster, thanks for all the insight, tips and suggestions. I went for a 33 mile ride today (personal longest) and really focused on keeping my cadence up and pedal stroke. I'm not messing with my saddle until my boyfriend gets a chance to look at it and help.

To answer a couple questions posted in the replies: I use clipless pedals, and while I have a computer, it doesn't measure cadence. Today, a couple times when I guessed I was at about 80 rpm, I counted each revolution for 15 seconds (using my watch) and multiplied by 4; my guess was right. So I have a comfortable cadence at about 80 rpm.

I resisted the temptation (mostly) to shift to a higher gear, especially on the flats. When I succumbed to the temptation, I could definitely feel myself falling below 80 rpm and, unsurprisingly, felt it a lot more in my quads.

I focused much, much more on pulling up on my pedal stroke and could feel it much more in my hamstrings (not a bad feel). When I felt my quads getting tired, I noticed that I had a) lost focus on pulling up and was relying on the downstroke too much, and/or b) was in too high a gear and was mashing at too low a cadence.

To conclude: So far, my legs feel GREAT after today's ride! Pedaling at a higher cadence did not seem to slow me down too much, but my speed may have been maintained at or near "typical" speed by pedaling more efficiently (esp. upstroke). I will continue to focus on these things and see if it continues to make a difference. Thanks again!