I assume you are using the vacuum switch to get throttle controlled kick down.
It may be that the vacuum switch is the culprit in the OD chatter.
Try bypassing it and see how it acts.
I scraped the vacuum switch on my setup because I found it really wasn’t necessary.
If I need that much acceleration I reach down and turn OD and/or LU off with the switches on my shifter.
The vac switch just added a bunch more junk that really didn’t need to be there.
I have adjustable pressure switches which lets me set the speeds I want, and I plumbed the pressure line from the governor port up to the back of my intake where they are on a bracket on the passenger side of the distributor.
This way I can change the switch settings from under the hood.
Here’s the switches on the shifter and the adjustable switches from NOS in case you are interested.
I’ll be in and out for most of the day, but at very least see any questions you might have this evening.
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