Rachmaninoff Prelude in G Minor Op.23 No. 5

[silyaznfoo]

I'm currently working on this piece, and there are a few places I have trouble. The first one is in the top voice in measures 18 & 19, I have a handspan of one octave and it is difficult to play the correct notes clearly and quickly. The next part is in bringing out the middle voice from measures 42-47. And finally, the jumps in the coda starting from measure 72, because by that time my hands are fairly fatigued. Does anybody have any tips on any of these three parts? Any help is appreciated.