I have recently purchased a ferris IS2000z 60'' w/ 29 hp kohler. I am having an issue with it leaving random uncut blades of grass. it was a demo with less than 100 hours, so i purches a set of oe blades from dealer still same result.I am a commercial cutter, but my cutting season is over for the year i'm just trying to figure this out for next year. Any help would be great. oh ya dealer had no good answer.