I have a 52" SCAG WB Hydro. When going downhill it sounds like it is going to blow the motor. It revs up very high and when I go uphill it slows to a crawl. Any ideas? I checked the belts and they all appear in good condition. I haven't done anything else except drain gas and added fresh. One of my workers says it's the governor that regulates the power and it should be acting in the exact opposite way.