Rytham problem

[Jdeadevil]

OK, this is very annoying, specially on Guitar Hero III. I cannot stand songs going off beat or notes going random (which happens a lot in GHIII). For example, I've just been spending about half an hour trying to AAA (on Stepmania) this really easy song. I think one of the only reasons my subconscious freaks out is because it can't handle getting AAA or sometimes a full combo. It's the same with Guitar Hero III, I can't get five gold stars on the second track on easy because my mind doesn't like me being special in any way. If I do happen to get five gold stars (which I've only managed to do for the first track on easy), it was just luck. I freak out deep down when I'm doing well by the end of a track, it's like that on all tracks and levels on all music games, I just don't get what the problem is, I'm doing everything right but they always have to give me the one little error, and then I'm fine the rest of the whole song because I know I've lost.

Other than practice and experience, does anyone know any good mental preparation advice for me?