Clara...

I'm working on this ... I have practiced it all different ways - according to what needs work the most. Although I *should* have started off by blocking chords, I didn't do that right away... I probably did practice H.S. initially - just to get the feel of each chord in each hand, how they progress, what changes, what doesn't - then the same with H.T. - how the chord changes related to each other... The hardest part for me is the descending parts - where the RH pinky replaces the thumb - I have isolated those specific movements - using my RH thumb as an anchor - both incredibly slow-motion, and quckly - just the change of thumb-pinky - and then, 5-2-1-5 as a quick grouping (I hope this is making sense) ... I just make sure I'm not practicing it the same way every time. I think - do whatever you need to do to get it into your system (the *learning* process), and then - whatever you need to do to get and keep the accuracy (the challenge with me).
Practice with
and without pedal (I hear and feel different things with each) ... One time, I was so frustrated with my 'sloppiness,' that I slowed it down and I made the 1-5 (or 5-1) changes without letting the key come back up. Sounds crazy, but it helped.
When I'm being super-disciplined, i always try to end a practice session of that piece with a slow-motion run-through (but I'm not always that disciplined).
I have no idea if any of this helpful or not ... but, I think you just have to pick a section and do whatever works to get it in your hands, as simplistic as that sounds. Take is a section/phrase at a time. In the end (better, while you're doing that), try to make it *musical* ... there's nothing worse (IMO) that a non-musical performance of that etude - especially when one is missing a ton of notes, LOL .
I'm sure there are more great suggestions from other folks here... Good luck!