Hi Scott,
I would like to know whether you have tried Under Options, click Do not import duplicates. This option will not duplicate import, unless if you want the imported information to replace or duplicate items already in Outlook.
For more information: Import Outlook items from an Outlook Data File (.pst)
Another way to import or restore only a few items from an Outlook Data File (.pst), an easier way is to open the Outlook Data File, and then in the Navigation Pane click and drag the items from Outlook Data File folders to your existing Outlook folders.
For more information on opening an Outlook Data File, see Open, change, or close Outlook data files.
You can also contact our dedicated Microsoft Community Outlook support where the engineers are more professional in Outlook client and they will focus on the importing .pst issue you encounter to get it resolved more efficiently.
Best regards,
Shyamal