I had a similar problem to this with my Rincon. When i hopped on it and drove off right away it would shift from 2nd to 3rd right. I would shift in a hgih RPM and when it got into 3rd it stayed at a high RPM and dint get any faster. Once it warmed up it shifted fine. We ended up finding out it was just low on oil! These Rincon trannies are really touchy. We took ours up to a Honda dealer and they checked the systems for us when we had this problem. So thats what i would do if I were you.
2008 Can Am DS450
PRM Baja Bumper and Skid
2007 Honda Rincon 680
Fuel Injected
ITP Mudlites
Hopefully some more goodies soon
1986 Honda ATC 250SX
Knobby tires all-round
otherwise.................... STOCK