I have a 54" zero turn with a 23hp kawi and this spring it seems to be shooting out clumps of grass. I have changed blades a couple times did not help. Going slower makes no difference. I am using high lift blades and don't remember it doing this last spring. The only thing left I plan on checking is engine rpm. Also tried totally cleaning deck and spraying fluid film. Keeps deck cleaner but still clumps any ideas?