MSD step retard issue

Ok, this is driving me nuts. Installed the MSD start step retard box, went to mud race. All good first pass, second pass good, third not so much! Nitrous system wasn't armed for any of the passes. Ignition acted as if someone was shutting off and on down the track. Wide open nothing etc. Checked all connections, wiring, coil wire ,cap n rotor, pick up in dist. Checked grounds and supply voltage all good. Wondering if start step is junk? Has anyone had similar problem? And where to go next? Thanks cory