Do you have a clamp meter (if you don't, get one).... Put your clamp meter around the cord for the tool. Slowly, engage the tool, watch the amps... if the GFCI fails before the requisite 15 (or 20) amps, it's the GFCI. If the GFCI fails while the meter says 23 amps, well then it's the tool, not the GFCI. Also, experiment with the tool with varying degrees of firing it up... read the meter... will give you an idea if it's the actual outlet, or the circuit.
