Strange unsuspected things can affect handling. I drive a Sprint Car on an Asphalt oval and just went through the process of laying down the battery from it's upright position. This required moving the ESC, receiver and fan. The fan had been shoe gooed to the the chassis but no room after battery lay down so went to a heat sink motor mount with the fan at the rear of the motor. Too close to the battery to mount on the front of the motor. It was a tricky mount to stay clear of the body cage and the left out-drive but got it done, (I thought). Ran the car and it worked nice. Ran it some more and it would turn to the left on acceleration anywhere on the track. Finally tore into it after trying to correct in other ways and found tiny witness marks on the edge of the fan where the axle pin at the out-drive had been hitting it. Turns out the heat sink had rotated slightly from where it started; probably from installing the body and the cage hitting it. Took the fan off and all was well.
It's the little things. Back to redesign of the fan mount.