Just use a plastic golf tee to plug the lines going into the cabin. If that doesn't get at least 18" of vacuum, disconnect the line at the vacuum pump and measure there. Then add lines until you find one or more that have large leaks.

You can also drive it and shift manually to confirm that the transmission is basically good and only needs adjusting.

Please break up your posts. Many here have old eyes and won't even bother to read the details of your post because the points run together.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.