GSP is a monster, surprised we don't see more fighters doing similar things like GSP. We see so many fighters gas really early and when comparing to GSP's work ethic, they probably can't keep up with him for 1 hour.
GSP is gifted athletically, but he puts the work into it. You see many gifted athletes in MMA or in other sports, who don't train like they should. BJ Penn is the perfect example, he is deadly when he trains at 100% but he doesn't have the mental game to do it everyday like GSP.
Instead of taking 2-3 months off after a fight, GSP is constantly working out and stays in fight shape all year around.