Make sure your throttle trim is set in the proper place. Chances are, since its a brushed motor, the motor is probably on its way out. They dont last long. Pull the pinion off, and hook your battery directly to the motor. If it doesn't spin any faster then when you give it full throttle, then there isn't any thing you can do. If it does spin noticeably faster, then see if you can recalibrate the esc. But since the esc previously fried, I bet the motor overheated aswell and lost some of its magnetism, causing less power and speed.