If the borrower voluntarily surrenders the vehicle on a delinquent loan, is the bank still required to deliver the letter stating that the borrower has 20 days to repay loan, etc.?

I appreciate any help! Thank you!

This will be a matter of State law. In GA, you have to issue the letter (10 days here) if you wish to preserve your right to sue for any deficiency.

The answer is in Article 9 of the UCC as adopted by your state. Review sections 9-611 and 9-612 for the timing of such notice of disposition of collateral.