Did you try the YouTube iOS app? You may need to change a few settings first, but I believe the YouTube app supports full quality videos - including 4K. Apple's built-in uploader from the share menu doesn't work that well.
In the YouTube iOS app, click your user image, then on the window that slides up, select Settings. Scroll down to uploads and confirm that full quality is selected for upload quality. Press the X on the top left to return to the main part of the app.
You may now press the camera button (next to the search button) on the top bar. It will ask for appropriate permissions. Try uploading from there and see if it works for you.
(I just tested this method and can confirm HD+ resolutions - also, I just noticed that this was a really necro'd post.)