Hertz has an "excessive miles" policy since a few years ago, mentioned in another thread. It is mentioned in the contract as, "Excessive mileage on a repeat basis may be cause for denial of your future renting privileges." Some longtime corporate renters suddenly found themselves on the Do Not Rent List.

You're better off doing the drivein special from NY to FL, with Hertz or competitors, and flying back. Or if you really want the roundtrip, go with National or Avis.