Im have this problem with my xstar. I have been away for two weeks it was working perfectly before I left but got back today and it is running strange.
It was set at 39KPH and I went to ride but now at 39 it revs alot higher and is going faster. If I put it down to 32kph so it is doing 4000rpm ( normal revs for the speed I ride) it feels a bit slower then I normally ride and the wake is really curling on the left side and a bit mushy on the right side.
Something similar happened before but it was reving more and going slower. I the end they replaced the transmission, fly wheel and prop shaft and it fixed the problem. Though I think it all came from the flywheel cracking.
The wierd thing is that when this happened before I was while I was away for a while too.
The only reason that I can think of is that maybe it hit the bottom while we were away as we live on a reservoir and the water goes down alot even though the dock gets moved alot.
Any way any advise would be apreciated!!