A friend has a Toro LX420 riding mower. He had to replace the blades, and the parts department did not have Toro brand blades, said that universal blades would work. Since he installed the blades he has had to raise the mowing height two notches higher than he normally mows, to keep it from scalping the grass, and it seems to be harder to steer.Could it be the blades, or something else that could be causing this problem ?