Lately my bike has been having shifting problems. When I am accelerating and shifting into 3rd and 4th gear it won't shift at all. When I try to upshift, nothing happens......the shifter will not go up any further and it won't go into gear. The shift lever is positioned fine and is not hitting anything. I have to stop accelerating and try it again. I looked pretty silly at the last Hare Scramble coming out of the tent and trying to accelerate and shift with the bike screamin in 2nd gear. I've tried different types of oils including ATF and Mobil1 red cap. Is this something with the shift mechanism or with the clutch. The weather is getting cold so it's about time to tear it down anyway. Any ideas? BTW..the bike is a 99 200exc.