Thanks for joining the Community today, @jimmy17.

Currently, there isn't a setting that will stop the check number to add when importing the iif files since it will depend on the data you imported. However, you can manually edit the check number when importing the iif file. Let me show you how.

1. Open Microsoft Excel, go to File, and then select Open.
2. Click the drop-down list for File type, then select All Files.
3. Select the IIF file you want to edit and select Open.
4. In the Text Import Wizard, select Next, and then Next and Finish.
5. Make the changes to your IIF file.
6. Go back to the File menu, select Save, and then click Yes.
7. Exit Excel.

Then, you'll get a prompt to save the IIF again. Select Don't Save. After that, you can import your file once again.

For your reference, check out this article: IIF Overview: import kit, sample files, and headers. This will provide you sample charts of how the IIF looks like.

Also, here are some articles that you can read to learn more about the transactions that you can import and export using Intuit Interchange Format (IIF) files: 

• Export, import, and edit IIF files
• Tasks you can do with IIF files

Additionally, feel free to read the topics from our QBDT help articles in case you need additional guides while working with QuickBooks in the future.

Let me know if there's anything else you need about QuickBooks. I'm still here to offer my assistance. Have a good one.

Confirmed that the old importer (the one that you start by hitting "Import without review") doesn't have this issue. It's also 100x faster than the new importer.