1. Open Mail.app
2. Click on the "Sent Items" folder under the "Gmail" folder
3. Click on the "Mailbox" menu item of Mail.app
4. Select the "Use this Mailbox for" menu item
5. Click on "Sent"
So now when you click on the "Sent" folder under Mailboxes, you see the contents of the GMail Sent Items IMAP folder, with the correct "To" and "Date Sent" columns. 🙂