Last season my 15f would always run 7K + 4 bars & speed was 65-65.2 gps with low fuel. This ski has had a bad vibration since I bought it after replacing many parts decided driveshaft bearing needed replacement, I had the dealer do this job in fall, in March I took ski to Florida (vibration still there but less noticable) & the ski ran 7K +4 bars, on a long run I saw it blip 5 & speed was 65.4 at best. I was wondering if it would increase in rpms & speed at sea level vs Wisconsin like my old Polaris.(that picked up 100 rpm & 1.5 mph) So then though maybe 4 strokes won't be affected. One week later I'm back in wisconsin & we have an 80* day in March so I went to the lake, now ski will run only 7K+ 3 bars & acceleration is a little less & 64.2 max gps low fuel. Thought maybe the extreme cold water or spark plugs, changed plugs the same, water now warm the same. I have got my speed back + a little extra with pump wedge & Impros impeller, but still at 7K+3 bars. After this long winded explanation is there something the dealer could have done when they removed the engine to replace the driveshaft bearing that could account for this slight loss in rpm?