The only way to know for sure if you need to change gearing is motor/esc/battery temps. The only way these can be accurately measured is with a IR Temp Gun. SO without knowing what your temps are, there is no way(unless your motor is scalding hot to the touch)to suggest a gear change. As for your spur gear, did it melt then break or just out right break? BTW, running 6s on a stock Maxx, be fore warned, you will have more carnage no doubt. Get ready to do diffs soon, you'll need the 1/8 diff conversion.