Put a trace on your gate and on your load and see if load follows gate. If so, it's because your gate is a capacitor, and you're seeing reactance in action at the frequency you're operating at. You may need to choose a mosfet with different gate response.
In the application schematic in the datasheet of the driver, there is no resistor between the driver and gate.
The resistor will cause a delay in conjunction with the gate capacitance.