2005 GTX 4 Tech/ is slow out Hole No

[05seadoo]

I have an 05 seadoo gtx 4 tec no supercharge. It ran great last year around 60mph took it out a month ago and it would only reach 48mph and seemed to just not top out all the way. I took out today and it would only do 30mph at 5500rpms and will not come out of the hole. Changed the plugs and there is no change ran it 45 mins and thinking bad gas. but no help. i tryed to let it idle put on digital rpms while it was warmed up and even less power rpm at idle and would 900 to 1450 to 1200 to 900 it is all over place and had new plugs. It seems to run even rougher like a miss when warmed up. new to this any suggestions