I think I've diagnosed my EGR problem...am I right?

I posted here a couple of weeks ago about a P0401 code (insufficient EGR flow) that is causing a CEL on my truck. I pulled the egr and it looked clean and functioned normally with vacuum applied to the top port. I know that two other components affect EGR function - the VSV for EGR and the EGR vacuum modulator. I pulled the VSV last friday and examined it. It appears to be funtioning normally when 12V is applied to the terminals - a definite click. Next was the modulator. As I understand it, the modulator contains a diaphragm that is connected via the larger bottom hose to the EGR valve. Being a diaphragm, should it pass both vaccum and pressure through the bottom port? Mine does. Both vacuum and pressure are passed through the modulator when testing out of the engine. Bad modulator? I know that the VSV has a much greater propensity for failure in this motor, but when my local dealer quoted me $179.00 for a new one, I balked just a little. The modulator is only $59.00. Am I on the right track here? All vacuum hoses are tight by the way. Thanks all.