Is blade tip speed the reason I can't cut at 7-9 miles an hour? Husqvarnar dealer say's it's 17500-18500. Blades are sharp, but it leaves spriggs of grass at that speed. Dixies are supposed to be 19000. Should I try to increase to 19000 or just slow down. I know it is federlay regulated at 19000. Iguess that possible 1500 or so make's the differance?