I would gear DOWN, based on what you're telling us (paddle tires + sand = more work for the motor). Maybe go down 1 or 2 teeth on the pinion. Basically, gearing should be based on your desired performance parameters, taking into account the working temperature of the ESC and motor. The bigger the pinion, the higher you're geared; higher gearing = higher top speed but slower acceleration. Smaller pinions = lower gearing; that means faster acceleration, but slower top speed.
If you're overheating, you're likely over-gearing (pinion too large). The ESC or motor will be too hot to touch. 180-185 deg. F is the hottest you should really go on a brushless motor. I recommend getting an IR temperature gauge from Radio Shack or Home Depot, or install the temperature telemetry sensor with your Tqi radio and iPhone/iPod Touch. It works great and you get up to the second temps without having to take off the body.
Whether or not you're over-geared depends on a lot of factors. What's the outside temperature? Are your wheels and tires larger than stock? What surface are you running on? And so forth...
You can also be UNDER-geared, i.e., having a pinion that's too small. In this case, your RPMs can get high enough to overheat the motor.
What you're looking for is a happy performance medium and reasonable motor temps.
Hope this helps...
