The only way you would be able to get a refund with respect to the car that you have is if it is presently under warranty from the manufacturer of it. I suggest that you carefully look over your paperwork concerning the vehicle that you are writing about to see if you received a warranty for it when you acquired it.If you did not, then most likely you will be responsible for taking care of the car's transmission problem at your own cost before you trade it in. As to using more gas than what you were told, the amount of gas usage depends on the individual driver and the driving conditions of the vehicle.