You stated your initial rpm/mph info was 3000 rpm at 55MPH....then you changed your driven gear and now show 3000/55 using the GPS. So, your first gear was correct? How many teeth? How many teeth on the new one?
3000 RPM sound high for 55MPH...but, I could be mistaken.
I'm a hobbyist. Not a professional. Don't be hatin'!