2000 Polaris 325 Magnum 4×4.

Recently, while riding, we’ve had the gear shift pop out of forward (high) and into neutral. The problem seemed to start out small, but has gotten progressively worse. It is now at the point that it will go into gear, but as soon as throttle is applied, it jumps into N.

I’ve tried adjusting the linkage with no luck, and have no idea what to look at, or to do next.

Any ideas? TIA.