Yea 2010 had alot of issues with this waiting on mine to fail. They say if you use low range alot this causes it but Im not sure. All I know you have to pull the tranny and put an upgraded kit from polaris not sure on part number I believe its around 700 bucks. My buddy just did his same issue.
polaris part #3235271. Mine did the same thing, bought the kit and fixed it myself. If your rzr has a build date of 05/17/2010 or earlier it has the bad parts in the transmission. The above mentioned kit is the parts they switched to after that date. Kit is about $600 canadian. It should have been a factory recall.