The 48 volt rating on your current motors is probably not the actual motor voltage, just a recommended supply voltage. It is probably about ten times the actual motor voltage. Most manufacturers give the actual motor voltage so you need the actual voltage to make sure you compare apples to apples. Do your current motors specify a coil resistance?
That said, yes you can replace them with different 3.2 amp motors. The motors should have a voltage rating under 5 volts. As a general rule, the maximum speed of the motors is proportional to the ratio of the supply voltage to the motor voltage. The supply voltage should be about 8 to 20 times the motor voltage for good performance.