Q: iTunes skips from song to song on own

It does this with all songs?  If so, if you play the same song that just skipped again, does it skip again at the same spot?  If it only skips some songs, not all, does it always skip on the same songs, or does it skip on random songs?

Do you use headphones on the Mac, or external speakers that use the Mac's headphones jack (audio output port)?  If you do, try disconnecting the headphones/speakers and listen using the Mac's built-in speakers, or other output that does not involve the Mac's headphones jack.  Do the songs still skip?