FT, when I first started riding many years ago, I noticed a phenomena -- namely, after I finished a ride of a certain new distance or difficulty, any attempt to replicate it thereafter was significantly easier (and anything short of this "epic attempt" would, too, be even easier than previously conceived).

I don't know if it was psychosomatic or if I literally "broke a (physiological) seal" for a given distance (speed, assent, etc.), but this phenomena proved invariable for me as I ventured out for longer and more arduous rides.

Let the body recuperate for a couple of days and try the same route again (don't wait too many days, atrophy is more harsh than a sardonic wife!!!)... what you might find is that at the end of 97.8 km that you have more juice and, thus, able to push on for a few more kms.