Hi, I have an 800 unforze from 2015, it goes back and forth but when I put pressure on it, something slips! It's just like it jumps on some gear or something!! Has anyone encountered the same problem

[2015 Z Force 800 53/Trail EPS]

Typically when one won't stay in a selected position it means either the linkage isn't adjusted correctly, there are loose or bad engine mounts...or the transmission has a bent or damaged shift fork. Make sure the engine mounts are tight and that the rubber is in good shape then check the transmission detents to the shifter gate alignment. If all that is correct and it still does it...you have your answer. It's in the transmission.