Preview slow to open TIFF files in Photoshop on macOS

After upgrading to Mojave, I had many issues, so I reverted to Sierra, which is able to work with CS.

One of the most frustrating issues was Preivews inability to quickly view jpegs and tiff files.

With this older OS, I am able to veiw jpegs as quickly as before, but TIFF files are still troublesome.

I noticed by accident a PSD file is processed much quicker that TIFF's, though I prefer to use this format for my layered files.

The tech at the store said something about newer OS's not havin

Why is this?

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