With the motor running and the clutch pulled in will it shift in to neutral?

If not this is most likely your issue is the inner clutch hub not spinning free and you need to put in a spacer:

http://www.suzukiquadracerhq.com/engine-13/trans-trouble/msg41404/#msg41404

I would also suggest Maxiam MTL-R  (80wt) for the trans oil.  It's the best we've found and if you buy it by the case on amazon it's about $7/$8 a quart.  If you don't want to get that pricy run type-F tranny fluid, either way change it often, like every 10-15 hours depending on your riding.