You can also print a reduction gear and add it to your motor mount if you need to .. 1 2 3 whatever you need to slow revolutions down when it ingangs with main gear.
You can run less voltage with a different battery as in going down in cells.. maybe a 1 cell lipo. but dropping voltage is going to increase amps needed to run motor.it will be a little less than half the speed its running at now..not sure that tamiya plug will handle that current