SOLVED.
For a purchased song from iTunes that wont play all the way through, I did this:
Deleted the file from iTunes, including iCloud (if you have it)
Went back to trash and removed it to the desktop and re-added it back into iTunes.
File that did play only 1:23 of 3:00 mins now plays all the way through without skipping ahead/cutting off the rest of the song.
Synced re-imported song back to iPod and it plays perfectly. Can't believe this hasnt been figured out yet! Or even Apple support suggesting this.
The hard part is figuring out which songs do this as I only discovered the tracks by random shuffle and thought wth? Why wont it finish playing? Good luck guys. Hope this helps.
Did you notice if the problem was with imported tracks or purchased only tracks? It seems all mine were purchased tracks from the iTunes store with the extension .m4p