I had a customer who would occasionally miss 2nd under hard shifts and occasionally get a "false neutral" with lazy shifts in 5th and 6th.
I made a shift kit that helped address the problems on his bike. (standard shift lever setup).
Here's an upgraded shifting parts kit for the 03 and later (at least till 2013).
New Shift Detent Arm - with a low friction microbearing instead of a riveted bushing. Doesn't wear out.
New Shift Spring - slightly more strength for better shifting.