My 04 wrx works fine all the way up to 5k. After that, the tach would take forever to get to redline. Particularly in 2nd and 3rd gear, once the tach would read at 6k, a rapid *click click click* noise would come from the engine. This is just a thought, but I think it would be my wastegate letting out exhaust. If anyone has had a similar problem, please let me know. By the way, the car is completely stock.
I agree, take the car back to the dealer. I test drove an 04 and redlined it by accident, and it rolled all the way up the tach fine w/o any hesitation. This is for the 5 speed. If your car has the automatic in it, then it could be a feature in that transmission b/c a lot of automatics will let you get close but will do all they can to stop you from redlining, especially with overdrive on. But get it to the dealer.