Originally Posted by Doctor Morbius
I'll second that, even though it came from Bicycling Magazine - the cliché of cycling mags.
PenguinDeD, it sounds like you may be mashing a bit much. Pick up the cadence. I'm not suggesting you spin at 115 RPM's but somewhere between 85 - 100 should do the trick.
Actually, the only way I can ever get my lungs to be fatigued is to sprint on flats or stand and mash up hills. No matter how fast I spin sitting down, I can't get myself out of breath.