My 2000 Chevy Cavalier shifts fine before it warms up, but once it gets warm it feels like it occasionally gets stuck in neutral in between gears. You can hear (and see) the RPMs increasing, but the car doesn't go any faster, and then it shifts (sometimes fairly hard) and everything is okay from...
More than likely it's your fuse. There is a fuse in the rear of your CD player so check that one first, and if it's not that check the fuse labeled as radio in your fuse box.