I purchased a 2008 GTI last year off a guy who had the impeller changed out. He said when he bought it off the orginal owner he thought the guy did some mods to make it faster. When I bought it I could get it to 60-61 on the water. Over the winter I took the battery out and then changed from champion copper plugs to new NGKs. Nothing else. Today I take it out for the first time this summer I'm getting 53-54 mph and doesn't feel as strong top end it feels lazy but runs smoother. I gapped the plugs to spec. The gaps on the old ones looks slightly bigger. I'm wondering if this ski had a flash Ecu tune done and removing the battery reset it to factory? Any suggestions??