I have sort of the opposite problem. On flats my cadence runs between 90 and 100 all the time. I have become accustom to riding in this range but I wonder if I am burning myself out. I start to fade at about 15 miles. I do this because it seems to keep my heart rate down more than riding at lower cadence in larger gears, but maybe that is what I need to do.

I am coming back from a nasty surgery that in the short term has reduced my lung capacity. I think in time I can bring it back through training though.