ORIGINAL: Super Mud
Probobly would make a difference, higher gearing will keep the motor from winding out and reaching the rpms too fast which will drain the battery.
I would think it would be the opposite. A higher gearing will cause a harder load for a longer period of time getting up to top speed which would cause run time to be shorter due to a higher amp draw from the motor.
Check the motor after running for about 1 - 3 minutes, no longer.......see if the temp of the motor is too hot. At the same time check the temp of the esc. When you get those temps right or at least close you should be good to go AS LONG as you have good connections EVERYWHERE.