I have a used GDSS w/18 hp. Kohler. The hydraulics are unbeleivable. I have adjusted for neutral on the sticks. I have changed the hydro filter. The fluid is old. With open throttle, there is NO cutting straight. Either one side or the other will suddenly grab and throw you off of a straight row. Down with the throttle, and blade speed, and you have to constantly play with the sticks to TRY and stay straight. Instead of lessening my workload, this machine has tripled it. My arms are sore at the end of the day, needless to say what the lawns look like! I have the owner's manual, and that is not helping. Maybe someone else has had this happen to them. This is my 1st hydro, so... Any and all help with this problem would be greatly appreciated. I sure hope that the pumps are not gone. Thanks, everyone, for your time.