1000rpm = 3333 full-steps/sec... never going to happen at 24v, you simply don't have enough volts to drive enough current through the windings to acheive that pulse rate... max rate at 24v is about 2000full-steps/sec = 600rpm unloaded, less at full load.

To get the rate you want you need at least 50v and preferably 60v drivers. And in any case your power supply is probably going into current limit if its only 120W so limiting the performance even more. Those motors are rated at 4.2A, your drivers can do 3A max so you are never going to get close to the motor's capabilities.