Sam has very good information posted about the transmission control systems including all the proper vacuum checks in the archives. I believe one should own and use a mityvac type tester to establish all is well with the vacumm prior to adjusting the modulator valve to compensate for probable vacuum problems. Or a cetain amount of transmission wear. If the modulator valve will not hold pressure with a test it should be tossed. These transmissions are also tuneable to a certain extent and that is a good thing. It was quite an effort for Sam to research, question and evaluate all he did. You get the results and usage of it for nothing. All you have to do is step up to the plate. This type of thing makes this site invaluable. It also increases your knowledge beyond what the average guy knows about transmissions. This is just my spin and beliefs on the subject.