Yep I bet the internal controller is toast!
But fear not, just open the motor rip out the controller and wire it up for a powerful controller such as an Infineon.
@ 60 volts it will do around 30 mph, go for 72 volts and 40 amp controller and you got yourself a 3kw, 3.5 peak beast and you will never want to get off your bike again!
Get yourself a battery capable of 40 -50 amps continuous if you can afford it, otherwise there is no point in spending money on an upgrade.
If spending money on an upgrade is not an option then get another internal controller and never set the regen to more than 50%! 30-40% for internal controller is better!
The pie is a seriously good motor if given voltage and amps!
Look around the forum in the pie mods section and you will find lots of information!