I've been playing this piece for just over 3 weeks. I am performing the piece Saturday and still have a lot of problems.

Learning the notes and memorizing was actually quite easy. But now I can play the piece at a high tempo (under 3 minutes), I am facing technical problems and don't have the endurance to keep the tempo high.

I also problems with dynamics and tone. I have tried many, many different approaches, but can't seem to get my ff loud en develish enough and my pp and ppp towards the end soft and bright enough.
The jumps are actually not much of a problem except for the big one into the g# minor chords.

I think I might be using the wrong technique.

The repeating chords are the biggest obstacle. I can't seem to find the right technique for it. If I play them fast I 1) play them unevenly and often miss the middle note, 2) get tired very often.
I have tried to use my weight instead and play with a loose wrist, but I can't get it at a decent speed. "bouncing" my wrist doesn't seem to be working either; I can't control the tone quality well in that way (not staccato enough, often quite sloppy). Playing them from up the keys with my arms I can really give them some sound, but it's too tiring to keep it up. Holding my arms stable and going up and down with my wrists doesn't work either; I sort of slam against the keys, causing noise when hitting the keys, and don't really make sound.

Any advice/experience would be very much appreciated.

Put the Cziffra and Horowitz behind you!

If you can't play the piece at a fast tempo error free, then my only suggestion is to slow it down until you can play everything in the suitable time without mistakes. As a member of the audience, I would rather joyfully listen to a piece that is 1 minute longer mistake-free than something that is 30 seconds faster than average but full of errors.

Just don't slow down too much because then it is equally as painful to listen to (I had to endure a participant in a recent piano recital--I was one of the judges--and he played Beethoven's Fuer Elise so slow, I wanted to go home and eat and come back without missing the next note)

I hope I am understood.