Have a 2012 - 48 inch Fastrack SD w/Kawasaki 24 hp motor. Specs say it is supposed yo mow at 8mph. I think it was close to that when purchased new but has slowed to max of 4mph. The dealer serviced hydros and replaced fluid and filters. I complained and he said it is doing what it is supposed to. Isn't it supposed to run close to 8? I have an old snapper lawn tractor 16 horse that will outrun this thing. I may make a trip to the dealer and measure his news units. What can cause this? Can I adjust this speed?