This sounds a lot like a similar issue I had with the Fitech and even with MS when I was running a distributor and the issue was that I was running the timing wire (the crank sensor in your case) too close and parallel to a coil wire going through the same hole in the firewall. Car idled and cruised fine but as soon as I put any load on the motor it would break up. I separated and rerouted those two wires and the problem went away. Remember if you can’t separate them it’s OK if the wires cross but not good if they run parallel to each other for any distance. So make sure the crank trigger lead isn’t running across coil wires or even the alternator charge wire (that one bit me too).
