I would agree, the PUMP is over sized, not just the motor. Your flow rate is probably around 85 GPM or about a 1.5 hour turnover. If you are looking to downsize the pump, you have a couple of options. Here are a few from cheapest to more expensive:

1 - Replace the Impeller and Diffusor with the 3/4 HP version
2 - Replace the motor with a two speed and run on low speed most of the time
3 - #1 plus replace the motor with a 3/4 HP two speed motor
4 - Replace the current pump with a 3/4 HP two speed pump
5 - Replace the current pump with a variable speed pump

Each of these options will save you energy costs with #5 saving you the most but then it costs the most up front as well.

Also, you didn't mention if you have solar or are planning to add solar at any point. That can make a difference when choosing a pump.