As I am one of few here with a speedometer, I have been trying to become more efficient at pedaling when the bike is near its highest speed.
The problem with the little bike is when it is at 13 miles per hour or slightly faster, pedeling and contributing any more speed isnt easy.
In my own experience, a wild fast pedal tends to make the bike rock, and dangerously close to its tipping point.
I've found that pedaling at only the very top 1/3 or 1/4 of the pedal cycle allows you to contribute to the speed and not over power the short travel of the pedal, and make it rock.
You add thrust, then you use the remainder of the path keeping your foot very lightly on the pedal, essentially resting for the remainder, or even back exerting to make sure you arnt pressing anymore.
The bike trail I have been using lately has several long smooth slowly sloping runs that I have been able to practice techniques on.
When done correctly, I can maintain 14mph for most of the slope without rocking. Its not easy, it takes concentration.