I have a Craftsman 6.5 horsepower lawnmower that is 5 years old. I have done the regular maintenance (spark plugs, oil, filter) every year. Is there any other maintenance needed? I am concerned that the blade may not be moving fast enough because the mower has problems mulching the grass now. I have the blade speed at its highest level. Are there any belts that need replacing from time to time on these, and if so, how hard are they to replace myself?