Does turbotax send a confirmation of transmission to the IRS independent from the IRS? I don't know if my transmission was successful, and still needs to be submitted.

Yes, TurboTax sends you an email stating your return was transmitted and then a subsequent email stating whether it was accepted or rejected. If you don't have this email, check your Spam folder.

You can also find out the date of transmission in Forms. Look for Postmark Report (Electronic Postmark-Certification of Electronic Filing). That form will show the date you submitted your return and the date it was accepted.

Is my return submitted