my bike shifts a little clunky

My 98 seems to shift a little sloppy when the revs are low. It shifts real good when I'm banging gears and running it hard, but if I am lolly gagging around at low RPM below 4000 it'll sometimes not go into 6th gear right. Or, if I'm cruising along in 5th for an extended period, and then want to hit sixth, it will many times get between gears. Not always, but it's enough that I am now expecting it to do it. I don't think it's anything serious, but it's annoying. I kinda figure it may be a characteristic somewhat of the bike, plus perhaps the detent spring is weak by now or something, or the shift star and detent are worn. I plan on adding a shift kit this winter, but at this point I might do it sooner. Chain is perfectly adjusted and in good condition, but the problem does seem to be getting slightly worse. It's got over 15,000 miles now, and I know pretty much the whole history of the bike and it was never abused.
Who has ideas or experiences??
One thing though, up front: I do NOT want to hear that it's my oil. There's nothing wrong with the 10W40 Honda GN4 that would cause this.
Thank you.

 

Going into 6th gear ain't no good idea at 4000 rpm. Too low. Engine wants alot more revs unless you're cruising slow at 1/8 throttle, eh ?

Change out old clutch fluid and bleed it if you have no idea when last done. Could be related to a clutch not fully releasing during some shifts, causing a stiff shifter and balky gear selection.

 

My bike also is clunky from time to time.
Changing the oil relieves the issue.

 

Oh yea, glad someone mentioned it: I changed the clutch fluid a short time ago, didn't make much diff, if any.
Oil gets changed every 1500-2000 miles in this bike. Just because I am insane

 

It could be the clutch is just getting worn out. Is it only getting stuck between 5th and 6th? The plates might be worn a little and you just neet to change out he clutch. Another thought is that the basket could be bad. While the bike is cranked and in neutral do you hear a slight ticking noise? sounds kinda like a low lifter noise. If you pull the clutch lever in the noise stops or gets real quiet. If so then I would say that your basket is bad and needs replacing too. Changing your oil out tha often is no insane. It just mean you like your ride and want to keep it running. I also think squirrelman has a good thought too. have you changed the fluids out lately? if not I would start there before changing out anything else.

 

The clutch on the thing does feel weak, and doesn't begin to grab until the lever is way out. I know hydraulic clutches are a little bit that way, but this is a little extreme. The clutch will be gone through, hell maybe in the next couple weeks, replaced if necessary as well as anything that looks suspect, shift kit will be installed, and we'll see what that does.
Yea, it's got a little "tick", but I never have pulled the clutch to see if it goes away....i'll try that next time I ride it.