Zipper Carnival Ride [Need Help]

Zipper model - I am stuck and I absolutely need help. The model is based off the one built by Greg Nuse at the Plains Indian museum. The cars hop the rails no matter what I do to reenforce them and the gears slip. I've tried making a proper gear box in the middle but it skipped worse than it does now.

I need a way to reduce friction of the cars and still keep the gear ratio the same as it is now. The model needs to run for periods longer than 3 hours. Any suggestions will help.