all gm motor controllers have regen braking, if it is badly connected and only makes contact ones in a while, rapidly. then it will vibrate and buzz.
make sure that all the connections are good to go, also make some test runs before doing the long jurneys.
if the brake levers are pulled then it stops the motor from getting any energy and therefore it will not run, and it will be hard to turn as the regen braking is also applied automatically.
cheers,
merry christmas