Cant get 8000 rpm

[CasTex]

I have 2015 GTX 260 on ~150 hours. On a bit wavy sea, I can get very hardly 60 mph, and the rev is max around 7100, I know something isn't right but no vibrations, no weird noises, so which part should I need to inspect ?

Note:
I just came across this impellar and wear ring, will replacing with this help ?
Amazon.com : SOLAS Seadoo 4-Tec 255 260 Impeller SRZ-CD-15/21A W/Wear Ring GTX-L RXP-X RXT-X : Sports & Outdoors

 

[pretex]

I would change your plugs first. Cheapest and easiest thing to eliminate. Have you ever had the supercharger rebuilt? If not, that would be the other thing to check is the slippage on the supercharger.

 

[CasTex]

The fixer said that its just about the wear ring. I asked does the supercharger rebuilt needed, he said "if no sound difference than normal, no needed"