I have a 2020 23 MXZ with the new Monsoon M6Di engine. I have recently had a check engine warning and the engine diagnostics states, "Knock Retard Limit". This has been causing the engine to slow on its own and making wakeboarding impossible since it won't maintain speed for more than 10-15 seconds at a time. Spoke with Dealer and they state this is generally a fuel quality issue. I have always used 91 octane. The Manual reccomends 93 octane but I don't know where to find this?? Since this I have used 91 octane ethanol free gasoline and also bought octane booster to try and boost the octane level. I am still having the issue and the boat is now in the shop. Any thoughts?