Well... In that version of Maybe I'm Amazed his voice a little weak... Don't you think? The original version is quite better...
And I'm sure that's not his highest note. I mean, that Yeaaaah can be really powerful, but is not a real HIGH note.
In the 1970 version when he sings ",,,and maybe you're the only woman who could EVER HELP ME...", in that part there are really high notes. In other songs like Balroom Dancing or The Pound Is Sinking, in the bridge of the latter, it's really high too. But I don't know when he sang his highest.