Zero Off surge

[lb]

The Zero Off in our 2009 Mastercraft 197 (MCX Engine) will some times surge up to 37.8 mph then slow to 34 it did this yesterday causing a fall as it slowed as the skier rounded 2 ball. we have randomly had this problem in the last 2 years that I have owned the boat then comes out of it for a while but only does it at 36. on a day when it is having spells it does not help to stop and shut down to reset. it does it in a mapped course and in open water. it is much worse using C3 than B2.

 

Any advice

 

thanks