Try one thing first and get back to us. Adjust the modulator with a pocket screw driver in until it seats. This will help us determine where you need to go. Even try back the screw out a whole bunch. See if it changes anything. I feel you have a modulator line pressure drop at the time you don't need it. Only a hunch, but worth turning a screw to tell us. We have many techs here that have a variety of experience to head you in the right direction.