Sounds like no vacuum assist. Have you checked engine manifold vacuum and the supply line being able to hold vacuum? The ILL shows the vacuum inlet off the engine manifold vacuum hose. There is a check valve there (2365). It may be bad. Using a vacuum gauge, check engine manifold vacuum and if good install a test tee at the booster vacuum inlet and see if the vacuum signal reaches the booster.
There is also an air filter used in the system (2363).
The hydraulics are in good shape, fluid clean and no frozen cylinders?
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