heres what i have dobne to my transmission and it shifts as slick as my bros 250r.
1)get the shift star modded
2)put a PVC pive section between the shifter and side cover so the shaft cant walk out away from the star inside.
3)shift forks and drum from an RZ350. These babies are hard to come by, but the forks have roller bearings on them instead of fixxed pins and the drum has a better profile. These things are sweet, but expect to pay good money for them if you find them.
4. Get every other engangement dog on the gears 2-6 machined off. This may be part of your problem. There are 6 dogs and the gear engaging into them is whacking against them. Whith only 3 on there it slides right in every time.
5) a billet shifter..that shock one flexes big time
6)keep the oil fresh.
With this setup I shift by just backing off the gas and lifting the shifter..no clutch, it just slides right it even with alittle throttle....cost me some money to do but was worth it