My son's 06 LTR 450 will shift from 2nd to 3rd on it's own when your on the throttle. It's ok when going super easy but get on it and it shifts. Anyone seen this before? Some insight before I tear into it would be helpful. Maybe a bent shift fork or a worn shift drum?

 

Those are the 2 gears that wear the most cuz they are 2 gears used the most.. I'd suspect a bad gear or 2.