I was recently in a pretty competitve 62m ride. The first hour I felt great. Had no trouble with the only big hill on the route. But around hour number two I got a bit tired. Had to fall off a wicked pace with some other riders. Hour three I was fine.
My drinks were potent enough but maybe I needed to down some gu to sustain my energy. Or maybe I need to just pedal harder and extend my training rides?