SPTT - HMMMMM....... I have worked through all of these problems over the last 6-7 years. Sounds like you might also have a bad egr valve. I would make sure that all of my vacuum lines and fittings are good before messing with the modulator. One thing you can check,.....take your air cleaner off, look to the back side of the engine. On the driver side of the intake manifold, back side of where the air/fuel mixture goes into the manifold you will see a rubber elbow fitting with a vacuum line that goes strraight dow. This is the vacuum line going to you trans modulator. REPLACE the fitting and check the end of the vacuum lines for cracks or hardness. Either replace the line or if it is long enough, cut off the hardened ends. You should also replace the rubber connector at the modulator to make sure that everything is tight and no leaks are present. I will dig through my manuals and stuff and see if I can find the destructions on how to adjust modulator. Again, I don't think I would touch the modulator until I was sure I had all my vacuum leaks plugged. Are the flpas for your HVAC system doing what they are supposed to? When the diagphrams break.....voils, vacuum leak. That's another handful of work! 5 or 6 vac pods and about $150 total. Let me know what you find out and I will be glad to help you and let you know what I have done. If you want, send me an e-mail direct.
Good luck