I have a Scott's L2548 which isn't mulching correctlly. It's leaving a LOT of grass clumps all over. Even when the grass is not high. I've checked that blades are sharpened, correctly installed, both cylnder's of the engine are working. Problem is worst when I'm mowing up the slight inclines of my yard. It appears that the engine doesn't have enough power to rotate the blades quick enough. Engine power drops a bit when engaging the mower blades. Help.