Par car shudder
 

A 2007 par car 48v electric (6-8's). Replaced the controller and accelerator. Still shudders at initial start up in the morning, after a long rest. Completely charged. And occasionally when starting up slowly. Smooths out when fully depressing accelerator. And runs good for a while. We can run 25 miles and still has lots of power. What can be wrong other than possible brushes. And about what cost? Thanks in advance.

What led you to replace the controller and throttle potentiometer? You are correct about the motor and the brushes. You most likely have worn brushes and the commutator of the motor needing resurfacing and undercutting. I will PM you with pricing.