fragile spur gears???

Hi guys... i run a, E-maxx with a feigao 9L, and 14 cells, 70/16, andd BigJoe tires...
Since I try to have more acceleration in programming my TX, i destroy all my spur gears... With 75% of EPA that works correctly, and when i arrive at 80% I begin to ear a bad sound... and some teeth of the spur gear are completely flattened... Is it due to the heat of the motor that melt the plastic spur gear? (my motor, axle and pinion are pretty hot, and my motor plate also... more than 100°C)
I run a RRP slipper, 70/16 ratio ... All was right until I tried to have more punch in modifying TX parameters...
Someone told me that it is due to my slipper, that is tightened too much... is it right???
I tried to add a fan on motor but it did nothing better... Do I have to run a steel spur gear with my alloy pinion??? I think that's it's not the way to solve my problem...
Please could someone help me??? Does someone know the best ratios to run my setup???