Maybe my jd dealer has no clue how to adjust the governor properly or something. I really dont know. I know I ran both mowers the same as I do my own machines and both would loose rpm and start slowing down going up inclines. I have the same 25hp kohler on our 160Z and that mower only has 10cc hydro pumps and motors but inclines or deep grass doesnt even phase it. The 31hp on our 460 is just ridiculous. I wish I had gotten the 29hp efi kohler instead.