Cannot upload ipod music to new mac

iTunes will only copy Apple purchases from your device, it won't copy music bought from other sites or that you've copied from CDs. Have you not got a backup of your content on, for example, an external drive that you can copy onto your new Mac ? Or if you still have your old computer then you should be able to copy it over from that : http://support.apple.com/kb/HT4527. If not then you will need to find a third-party program that can copy your content off the iPod.

Your iPod can only sync with a maximum of five computers. You have to authorize the computer to work with your account. To do this, go to Store > Authorize computer and fill in your details. Once you have done this, sync your iPod and your songs should move onto the computers hard drive. Hope that was help!