About Jem7V sustain
there are a lot of reasons! it could be gain, volume, bad setup, etc.
have you noticed the way steve sustains notes? that circular motion makes the note last longer (IMHO). If you're thinking about AIAUW there's a fernandes sustainer all over it!
about that high fret notes: it could be that you action is too low, or you don't fret a note totally 'behind' the fret (ie a part of your finger is nearer to the bridge than the fret)
well, hope that helps!
BTW bati has anything to do with Batistuta?