Awesome, thanks guys.
Tucking my elbow in does help (I swear, I never realised I wasn't doing it, it feels like common sense to do this) with the sour notes, but the thumb still explodes eventually.
Harmonics are much easier, now, still going to take a bit of practice...it appears I misunderstood what I was supposed to be doing.
Whoops, almost forgot:
Oddly enough, I found that running scales constantly helps with my endurance for chords.
Could you elaborate on this? Not too keen on the lingo. =p