I have a similar problem. I have a 1996 Honda CBR 600 F3. We just replaced 2nd gear and its adjacent shifting fork in the transmission (not fun, try to avoid). Anyway, the tranny is running great now, but at about 7 grand in any gear, the tachometer goes crazy and it feels like I'm losing power until I shift up into the next gear. We did put on a new chain, front and rear sprokets, but I really think this has nothing to do with the gear ratios. Another site said it could be a lose electrical connection and/or a bad battery, but we also replaced the temperature sending unit on the repair and I think this unit is about 7 degrees off the old one, show it shows up a bit hotter than what it is. Did you fix your problem, if so, how? Any help would be greatly appreciated.