Lets use this two words HT=hand together HS=hands seperately.I read this at an online piano book which i advice you to read.The max speed that you can obtain HT is the same as the speed that the slowest hand has HS.Check which hand gives you problem,so if you have not studied correctly HS,then HT will never be at speed.
My advice is that you should try to know what to hear before trying to play it SO FAST!.Study at a pace that you can think (and feel!inside you) the next movements,and do not make the study be mechanical or you will never reach high speed.
Also if you are trying to learn this piece and studied for a long time with no results (mainly because of incorrect style of play),drop it for 2-3 months and only THEN come back.
The piano sound is a combination and a mix i think of 4 different elements,the sound -(or rather an illusion )- of legato,stacato,tenuto and lieggero.I know that there is the full stacato half stacato,heavy legato,legatisimo legatisisimo .and lieggerisimo plus others,but the combination of these 4 styles -and the mixes that can happen- for the style of sound,are what create the sound we want to hear.
Try to know the required sonority you want to hear,relaxization must be your first natural thought.As for advice tell us more about your style of play,you play with weight?Are you one of the pianists that sit lower on the bench?(like pollini for example or horowitz?),or are you one of those who sit higher on the bench(richter comes on my mind)? You use flat finger style when you play fast passages?Tell us more about your style when you play.
Example if you feel that you keep raising your shoulders to play that could mean that you play too near on the piano and your hands are blocking your mobility.You feel tired only at that specific part of the work?