The GM V6r is rated for up to 12 volts, so 7.4V input will not cause any long term issues with this esc. The motor can handle 7.4 volts all day long with the right gearing. Running in grass using the throttle as an on/off switch is causing the heating issues. With heating issues comes brush and com arc. If you replace the brushes, cut the com, and use a more conservative gear ratio, you will be fine.