If you ran the motor right out of the box I would recommend trying it again, but first cut the comm and put new brushes in. Sometimes the comm is not true from the factory which will cause brush bounce and excessive arcing which will wreck your brushes and lower your max rpm. Those numbers on the can are pretty bad though, you certainly could have got a bad motor. If the car runs out of speed really fast on the straight keep gearing it up, undergearing can also cause problems with heat since the motor is very inefficient at high rpm.