I just receive my new toy, a Garmin nuvi 755T GPS Nav. I've done a few quick trips with it, working the kinks out getting ready for the big trip.
I found a web site http://www.takitwithme.com (Take It without the "e") that allows you to export your Google MyMaps to the Garmin as a Route. So I have my trip to Yellow Stone figured out day-by-day and am working to save them as daily Routes. It's actually why I bought the 755T over the 265wt, the 7x5 series supports Routes where-as the 2x5 only does point-to-point.
It's a neat web site. I was having a minor problem so I sent some feedback to them at 10pm Sunday night... and the developer replied to me in less than 15 minutes!