I think that 20 amps at 48v might be a bit high for that motor. Try 15 amps, and, if that's not enough, solder the shunt a bit.
I'd use the opportunity to update to an LCD controller. Any 48v brushless one will work. I can't remember if the Tonaro has hall sensors, if so, you have to get a sensored one or dual-mode. Normally, the controller and panel come as a set, except from BMSBattery, where you have a choice of panels, sp order separately. !5amp 48v controllers are not that common. Conhismotor sell them, but theirs doesn't have the connector for the wheel-speed sensor, so you won't get a correct speed reading. You'll have a motor speed indicator instead, which could be useful on a crank-drive.