What iOS / iphone app can provide turn by turn navigation of a pre-planned (mostly on road) route (stored in GPX or TCX file)? Voice features are nice, but not mandatory. I've found many apps that will track my ride, or display a route and my position, but none that will direct me when to turn to follow the planned route. This would be very useful when training for an event where gpx files have been provided, or exploring new routes that I plan to ride in unfamiliar territory.
I'm ideally looking for something like the android cue sheet app.