Re: G string sustain
Basswood and a floating trem should STILL give you adequate sustain, given that you're probably plugged into a high gain amp with pretty hot pickups.
How's your action? It sounds a little like the note may be choking out a little - lack of sustain, weird overtones, only happens as you get onto the higher frets... Maybe raising your action a smidgeon would get it ringing out clearly...? Also, does it continue to happen at the 24th fret? How about the 22nd or 23rd? If it's bad from 7 through 23 but comparable to the other strings at 24th, it sounds like the saddle might be too low and the string's choking a bit on the 24th fret (you could shim the saddle slightly, or just raise the overall action - if it's the saddle, I'd bet on a radius issue and the D string is choking a little, too - that or you have your low E action higher than your high E). Otherwise, if it's bad up to a point, but then good after that fret, the fret where it suddenly gets better again may be a little high.