1. Have you tried to resetting your iPod ?
2. Try another iPod and see if it happens with another iPod.
3. Plug in your iPod to iTunes and check for Software and Firmware updates.
I don't think the problem is your car, it's the iPod.
I have had the same problem before.This year on the way to the Dragon my iPod just stopped playing after 8 hours of driving. I stopped for gas reset it and have not had a problem since.
Resetting iPod Classic is pretty easy; here's how:
Slide the Hold switch, the switch at the top left of the iPod, to "on" (so it's showing the orange). Then slide it back to hide the orange.
Hold down the Menu and center buttons at the same time.
Hold them for 6-8 seconds, or until the Apple logo shows up on the screen.
Let go of the buttons at this point.