Electric or Nitro, gearing works the same. Now going from 14t to a 13t pinion really will not be a noticeable difference, but if you do the math it'll be about 7%-8% slower, but inversely have that much more torque, which *should* relieve some load on the motor and reduce the temperatures.
However do keep in mind, that free revving an electric motor (brushless usually) at WOT at relatively high voltage or for that matter underloading one is supposed to heat them up as well. That means if you go down in pinion size and almost to the point of the smallest possible, and the motor heats up even worse... you know the motor is not running with any kind of real load on it. What that means is you'll notice your motor top out in like 2 seconds and your truck will move pretty slow (it will have butt load of truck-pulling torque though...). Just a little reminder.
But yes try a pinion 1-2t smaller and see if that helps. I'm assuming this is the HV Maxx 4.5 motor, so I'm a little surprised it would heat up running in a 1/10th 2wd truck, unless the internal gearing is taller than I am aware of.