Go to Engineering mode, and then there are several options to choose from, one shows satelite details, etc. another shows your relative ground speed
(have to calculate that as relative cause you might be airborne, thank goodness for satelites at a moment like that)
I've found that getting into eng mode can be tricky...might require several attempts.
1) Push Nav button then release
2) hold upper left square button (around main knob) for 5 seconds then release.
3) Hold upper right square button until screen enters Eng mode..