JC, the first thing to recognize is that Op.23,No. 5 is not forte throughout. Most of page 1 is very quiet--a perfect time to relax. On the last two measures of that page, be sure to use NO pedal. Except for two brief accents on page 2 at ff, the rest of the page is either f or p--yet another place to relax. Also realize that in the f section of that page, only the scalar octaves are loud (voicing tops with the 5th finger especially). Play them legato using fingering 4-5-4-5 in the RH. The staccato figures in between are no more than filler notes played mf, although not marked as such. Why? Because they have no melodic role whatsoever and are merely background.
The middle section is totally lyrical. The LH produces a quiet lake effect with its arpeggios. The RH is chords stressing the uppermost voice with the 5th finger. Dynamics range from ppp to mf. Nothing loud, super energetic, or exhausting there. The real work is bringing out the lovely inner lines.
The last two pages are the most challenging, and the dynamic is mostly forte. With fatigue setting in, its sometimes difficult to play those last five chords of the 2nd, 5th and 6th measures of the last page evenly in rhythm. You need to watch that. Finally, many fail to relax in the coda believing that the passage goes like a house afire. It does not. Put the metronome on in tempo and you'll be surprised that you might have been rushing it. The note groupings in the RH of the coda are not at all what they appear to be in the writing. In fact, you have to mentally think in the 3rd to the last measure that the last two 16ths in the RH are connected as a group to the first two 16ths in the 2nd measure to the end. And in the middle of the second measure to the end, the 6th, 7th, 8th, and 9th sixteenth notes also are one group. If you think of it that way, it will be more relaxing to play. There is NO pedal in the coda.
So paying strict attention to the dynamics in particular, keeping background notes relatively quiet, and keeping the tempo accurate throughout will work toward helping you maintain your stamina in this piece.