I've had this problem for quite sometime and it doesn't occur enough to annoy me or keep me from riding, but I have a feeling I should probably try to figure out what is going on. When I am in my upper gears (4 & 5) and really revving the engine either going up a hill or in a straight line the transmission will randomly downshift one gear. I have a habit of shifting somewhat quickly (using the clutch) so at first I was thinking that I am not quite getting it all the way into gear and it's just slipping back down, but I donno. Sometimes I can ride all day without it even happening. I have the stock clutch still in the bike, but it never acts up and works great other than this. It may help to know that I have replaced the stock gearshift with a billet direct connection one. This NEVER occurs riding trails or anything like that, just when really revving the engine out in a race setting. I was thinking it could be the shifting forks, but it's not getting worse. I'm really confused with this issue, any help would be greatly appriciated. Thanks in advance!