Thanks Restro I'll give that a try.
I did adjust the valves to .006 and cut an acre this evening. The valve adjustment seemed to help a little bit, but I was still experiencing some power loss.
I'm used to cutting this lawn with my 17hp GT275. On the 275 I can distinctly hear when the governor is engaging while mowing, but I can't really notice the governor on the 777. Could this be part of my problem?