Run it in a lower gear, but at the higher rpms that you are running in 5th gear.. If it does it then, it could be the rev limiter, but it could also be the valvetrain...
Yamaha has inherently soft valves, and after 5 years of service, they are more than likely worn out. You "might" try just changing out the valve springs and see if that helps. It sounds kinda like you are "floating your valves" This condition is caused by tired valve springs..
Another thing to consider is whether your air-filter is clean, the proper heat range of sparkplug, (you could laso try running a colder plug) clean your fuel filter, take the fuel bowl off the carburetor and clean it out well (carburetor cleaner dont get the stuff out of your bowl....)..
Anyway, try all that first!!...

 

Stay away from the 'shrooms man.

 

when you took apart your carb you probably forgot to do something..... Clean Your Jets Too
i dont know how similar your carb is to mine but start by taking the bottom of the carb off then there should be two gold screw looking things, one is in the middle and one is a little to the side the middle one is called a main jet be carful by using the right screw driver or wrench and take it out and blow air through it then look at it up to some light keep blowing air through it until its clean. the other scew is the pilot jet it controls idle take it out by doing the same thing as the main jet. when theyre both clean put em back in with the bottom of the carb and hook it back to the engine and air box and try it out if it aint that it could be air leaks, rev limiters, dirty air filters, too rich or too lean jetting, valves, running out of gas or with gas turned off, water in gas or oil, need to change oil filter and strainer, out of oil, or your silencer is plugged up

hope that this all helps
i hope im not too descriptive either

 

When was the last time it was serviced?? It may be as simply as insuffecient valve clearence. When it gets good and warm, at higher RPM, it's floating.

 

well i put the muffler baffle back in the muffler and that helped out alot, i can run at high rpm and it quit doing it, but now when i am in a high gear at a low rpm it spits and sputters.

 

by the way, i do know what all of the jets are in the carb, i know what the main jet looks like and i havent been near any magic 'shrooms. i have cleaned the carb. many times.