just getting a better battery will do wonders for that truck. increased mah rating means increased amp output also in most cases. therefore a larger mah battery will increase not only run time, but power. this is done by simply being able to keep up with demand. if your truck requires 40amps but the stock battery can only produce 20amps, the voltage will drop and slow the motor speed down. if you can keep up with the motors demand then the battery voltage will remain where it should and you'll be consideribly faster and have more torque to boot. check out some good side by side 7.2v packs and a decent peak charger. i kind of got a soft spot for the dtx4200's. they've worked very well around me.

if you need something cheaper and easy to get anywhere, drop by a radio shack and pick up their 3300mah nimh.