Not gear related, but if you're going up and over Kentucky and Tennessee, believe those signs that tell you to downshift rather than ride the brakes while going down the mountains.  If you don't, you'll find yourself with no brakes before you're into Georgia.
Steve/RRA

Two things I like, stop leak and water pump lubricant.  Add the lubricant before you leave if you have room to do so.  Make sure the bottle says it has lubricant.  This prolongs the life of your water pump by lubricating the gaskets and "O" rings.  The farther south you go the hotter your coolant system will have to work for a given task.  

The stop leak, I like for that "OMG that isn't a bump but a pit" in the road that you can't avoid that slams your frame down so hard the radiator wants to separate from the base.  Adding a little saves your from that auto parts store stop and replacing a radiator on a trip and allows you to carry on until the timing is better to do so.

Before you even ask, yes I had this happen on Japanese cars.  

Tj