With that high mileage I would remove the transmission pan, if it’s clean no metal, change the filter and fluid.

If your model has the mode and B+ switch it complicates the diagnoses, adding the up shift delay actuator to the equation. It can also be valve body related K1 and K 2 accumulators.



If you still have a problem check the vacuum going to the modulator next.


Install a vacuum gauge directly to the modulator vacuum hose, with the engine running on a healthy there should be a steady reading of manifold vacuum present 14” to 22”HG. A quick opening and closing of the throttle should drop the vacuum to below 5” if not fix the vacuum problem first.

Engine vacuum is the load input signal from the engine to the modulator. Under a load condition, normal driving from a stop to wide open throttle, vacuum must drop, if it doesn’t the transmission will have a delayed, chattering, slipping up shifts. The vacuum modulator job is to increases working pressure base on a vacuum signal.
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