I have a 72" dixie chopper and as the grass discharges the back part of the shoot it is diving the grass into the ground and leaving a line of grass behind. It does this on the return pass where i have thrown the grass in on the previous round. I am mowing the grass at 3.5 to 4 inches tall, and does it with single, dual factory blades, and factory blade on bottom-gator blade on top. Have checked tire pressures, level of deck, don't see anything bent. Any suggestion ?