[What's_nitro?]

I think the main reason behind your temp problem is the excessive wheel spin in the soft sand. Lots of people run a 9xl/4s combo in their trucks and have no heat issues. You could try 5s if you already have the battery. It would give you about 35k rpm, up from 27k rpm. 35k is just about at the acceptable "efficiency limit" of the Feigao motors. I would probably start with the same gearing you have now. You'll need to keep the motor loaded even more on 5s, otherwise it WILL get hotter from running high rpm all the time while throwing sand.