I race stock truck and buggy. In these classes, its all about freeing up the drivetrain. If I take the pinion gear off my motor and spin the tires, it feels like they spin forever. Also, gearing for the main straight is the best way to find a ratio. I've found and been told by the owners of AXIOM and BIRDMAN that as long as you're not getting soft before the end of the race, don't worry too much about the heat.
If anything, polish the bushings and shafts of your motor and that will make a huge difference.