FIXED IT! I had the exact same problem as mentioned above ("System says 4.3U is installed but then still tells me I need to update and fails). This was a problem to me because I wanted to access the Shop channel to get Netflix. I solved this by using the SmashStack exploit to load HackMii. From there, I uninstalled BootMii/IOS. After that I went to System Settings and successfully updatedby gstep - Homebrew General