Pulled the electric motor out of the motorcycle and pulled it apart to see what it looked like inside, partly because under high load the motor gave a little chatter so I thought something might be up with it, turns out the commutator has
"threading" 
Instead of normal wear.
So I'm going to take it in and have it turned, crank up the spring pressure (already part of the plan) so I also spent a bit of time V-grooving between the commutator bars to help reduce arcing.
I would like to upgrade the brushes but I didn't find anything other then stock golf cart brushes.