That’s an incredible set of Trojans you have there! Mine did that with a reprogrammed controller and stock motor and same set of Trojans. Little better with blue motor only about 7-8 miles range though.
Now, lithium volt conversion is getting way better speed and range on stock motor and programming.
My vote goes to lithium even with the growing pains. Less weight, more power! What more do you need to know.
Did you change the tire size / ratio? Larger tires will throw the speedo off. Not sure you could put rims and tires big enough on these carts to get 9 mph difference, but 4 is possible.
A 2002 with no parts changed is a little hard to believe.
Are you looking to calibrate speedometer?
It’s a simple change in controller.
A slight possibility of magnet damage that could add 25% speed.