The first thing I would do is check the deck for level and pitch. You'll want to make sure that the tires are set to the proper psi listed in the manual first (typically 10 to 12 psi, not the max listed on the sidewall). The manual should also list the proper deck pitch and the procedure for adjusting it. Sadly a lot of dealers, in their haste to get things out the door, just keep tires at their shipping pressure and don't bother to level and pitch the deck properly.