I was inspired by the great info found on this forum and many similar forums. I did the 5.1 firmware mod and just couldn't live with the loss of some functionality. So I recently created a small device from $15 worth of parts that enables ALL of the factory NAV functions even while the vehicle is in motion, with any firmware at all. You don't need to make the 5.1 disc, it will work with 6.1 (and probably all future versions) just fine. It will most likely work on a lot of other vehicles and NAV units too. You can read all the details on my mod site here:
WileETundra's mod site
Scroll down to report # 16 - NAV Speed Pulse Generator
Hope this is helpful to some of you. Many people have asked for a solution so I am sharing. Thanks to all of you for sharing too. Let the modding begin...