Just one question. Is your game a copy?
It's noted on GH fan sites that some people who don't even bother to grace buying this super game are getting the glitchy problems due to the cunning programing Harmonix have used to stream the game if it's not on proper media.
I've only have encountered this problem about 3 times while using the supplied reviewers disc, but it was mainly down to my PS2 being the first model produced & the DVD lens needed cleaning correctly. Since then I've got the full retail release & have not encoutered that problem