Kingquad 300 jumping out of gear

[hrbrpilot]

While hauling a small trailer of hardwood, my Suzuki 300 kingquad began jumping out of gear. It does this in all ranges so I believe the problem to be in the main gears. It rides normal without any load. It has never done this before during the same annual task. Anyone have any ideas. I'm thinking it is simply a matter of making an adjustment somewhere! Scott