I have a Husqvarna YTH20F42T and it loses power when I push the gas pedal all the way down and also reverse is very slow. I have changed the oil, air filter, fuel filter, spark plug, drive belt, and deck belt. The mower works fine on a level surface with the pedal pushed half way but will not speed up when pushed all the way down. I am curious what else could be the issue the motor is running fine and blades will engage and work fine. Could something just be wrong with the transmission?