Try setting your high speed screw richer (note where it's set before you do).
If it still runs well, you might have had it set a little too lean.

If it blubbers at large throttle settings after doing this, go back to the previous setting. Mixture isn't what's causing the heat.

My HPI Savage always ran at 290-310*F when tuned properly. Monster trucks don't always do a good job of ventilating the engine well. Do you have a hole cut in your windshield?